Outside, pretty much none. Indoors, above 2.5-3 hours I’ll wear bike shorts over my bibs.
Assuming we’re talking about a road bike. My tolerance for riding not hard on my TT bike is not very high. It was more tolerable when I was racing long course triathlon though.
For me, saddle discomfort was a big factor in jumping over to a recumbent. Had some hand numbness/pain on long rides that also contributed to the decision. Possibly fixable with different seat/fit, but now don’t want to invest in the experiment. Besides, why would I want to ride a slower bike? 
I’ll try and keep this short…
For me, putting together the info from 3 different bike fits, as well as a bit of a eureka moment about core engagement and pelvic tilt, was the game changer and I am largely free of back and saddle pain these days. I can still get a slight ache in my back after about 3 hours, and I get a little saddle pain in >2hrs on the trainer, but they are very manageable.
I’d wager that your problem is solvable, but it will take some time. Keep a journal and be methodical.
Thanks @RecoveryRide
Can you say more about your eureka moment with respect to core engagement? What did you discover and how have you learned to engage your core?
This sounds like something that would be beneficial, and yet I’m a bit lost on what to do
Another “none”. To me, it’s a combination of correct bike fit, and then proper shorts/chamois and saddle combination. This is as individual as running shoe/running sock combination - there’s thousands of combos, and no two people are alike. For me, a chamois on the thinner side of “medium” and a bare bones flat, skinny Selle Italia seem best, which is counter-intuitive because I’m skinny as hell with zero padding in that area. I’ve tried other saddles, and they feel horrible, especially the ones w/ holes. I’m horrified by the ones with the nose angled down at 80 degrees, but apparently that works for some. My criteria is that if I can ride 3-4 hours and never once think “man, my butt hurts”, I have the right set up. I recently added a rear rocker plate to my Wahoo set up. It changed the front wheel height just a tiny bit. Within a week I had the first saddle sore I’ve had in 30 years (Voltaren gel and hydrocortisone cream work great for that, btw). It was the only bike I had that wasn’t a Selle Italia, so I immediately bought one on ebay, adjusted the front wheel height (with an old cycling magazine), and problem resolved. So you may have to think outside the box and go with a combo that at first glance wouldn’t seem right. There are a ton of barely used saddles on ebay and Facebook marketplace. If you buy and try and it doesn’t work, sell it to the next person. As for core engagement, “core” typically refers to your Transverse abdominus muscle, which runs like a wide belt across your abdomen. It doesn’t take much to engage it, you just have to do it right, or the other ab muscles (rectus abdominus, the “6 pack”) will kick in and take over. Lay on your back, knees bent, head resting comfortably on floor or pillow (if you lift your head, rectus kicks in). Now pretend you just over-hydrated on your favorite beverage and there’s no bathroom within a hour’s distance. Yep, just imagine holding your bladder or stopping the flow mid-pee. That right there is your “core”, at least the front side (glute max, med and min as well as some small muscles around your spine comprise the rear portion). You should be engaging your TrA with any exercise you do - squats, deadlifts, planks, push ups, CYCLING etc.
I appreciate your feedback and want to learn, but I’m not following this example. You’re saying your pelvic floor is your core?
It’s an essential part of your core, yes
Thanks. I’m just not sure I understand how I’m supposed to flex that for 3 hours since ke gels are seconds long, not minutes or hours.
Visualise the area of your stomach below your belly button but above your pubic bone. If you try and draw just that area of your stomach in without drawing in the section above your belly button, you should engage your transverse abdominis (sp?). Don’t worry about what if anything actually moves, that’s not the point; it’s trying to activate your natural ‘belt’ around the midriff. It’s not a kegel, just a sense that the core is engaged, active, dynamic - it’s not passive.
The sensation (and my eureka moment) is that your pelvis is rotated forward subtly by this motion, and that your body weight is supported by engaged glutes, engaged TVA, and falls forward not through your upper body, but through the pedals. These 2 videos are worth watching:
This is one of those things that is incredibly hard to describe in words but once you feel it it’s ‘aha!’
^^^what he said. doing a really good TrA/pelvic floor contraction during core exercises (planks, clamshells, single leg bridges, squats, deadlifts etc etc etc) will develop your core to the point that it engages to the proper degree when cycling, running etc. So if you think of doing squats w/ heavy weights for 10-12 reps to develop better strength and power on the bike (where you’re doing 1,000s of “reps” in a 3 hour ride), doing the kegels and core ex’s for seconds during core exercises will help the proper muscles engage while riding. hope I’m making sense there. A great reference for cycling specific core ex’s is Tom Danielson’s book https://www.amazon.com/Tom-Danielsons-Core-Advantage-Strength/dp/193403097X/ref=sr_1_1?crid=32SMPZC2MP5CV&keywords=tom+danielson’s+core+advantage&qid=1654271470&sprefix=tom+danielson%2Caps%2C117&sr=8-1
Thanks @RecoveryRide and @AustinPT - sounds like I’ve got some things to add to my routine. 
the older you get, the more essential it becomes. I’m about to hit double nickel, and I make “old man noises” every time I get up from a chair. Core exercises are the only thing keeping me mobile. Start now!
Me knowing about my pelvic floor and kegals is the tell that I’m up there too!
went to the store yesterday.
Aaaand… they’re not actually partnered for the IDmatch thingie from Selle Italia. Haven’t been for years.
explained my issues, went home with a SQlabs 612 R for testing. Gave it about 3.5h, taking care to follow their direction for setup and adjustment.
No better, for all the marketing 
And back to the shop it goes.
I think my pressure point is further forward up the nose than the usual depressions and cut-outs assume.
Have you had a full bike fit by a reputable fitter?
Bike fit is only part of the issue in my experience. I was fine on a bike when I was young. Could ride for hours no issue. Started to ride again at age 55. It took a long time to be able to ride to any degree of comfort despite having a bike fit. I ended up having to sort out what seat would work as I ended up with problems ie blood in urine and numbness from riding. This eventually was resolved with an ISM saddle, PR 1.0. New bike, bike fit and same saddle ended up with saddle sores. More small changes on the seat with angle etc. All lots of small tweaks with incremental stages. Also switched bibs a number of times. The seat for me was a major issue. Everything else was minor tweaks which all helped comfort. Likely took 4 years or so to really say I was comfortable riding a bike for 4-5 hours.
I would still start with a bike fit but I still had to play with seats and angles of the seat as well as just where to sit. Learned a lot where my sit bones were and how to adjust. I dont know if it makes a difference but there is a definite change in where I sit if I am on the drops or am riding more upright. I tend to ride a lot more on the drops and found over time I really had to work a lot on my core to be able to be comfortable in that position. I currently dont have any seat issues at this point in time so I do think you can get to the point of comfort.
Had a good day in the 100. Gravel King SK+ 43” with Cushcore inserts at 35 psi was a perfect choice. Waxed chain (Silca Super Secret) held up well through dust, water and mud. We made a tactical error waiting out the rain in Madison as the course just got worse.
I saw people mentioning sit bone widths up above. Measuring sit bones sounds great in theory but we don’t sit on the sit bones in the road bike position. We sit on the ischiopubic ramus. See the pelvis sitting on the saddle:
I’ve been riding road bikes for 40+ years. I’ve had a few issues. What has been a game changer for me lately has been Assos shorts. Their pad is unique. It’s like the reverse of a cutout saddle turned upside down so you get relief from the shorts. I combine that with a cutout saddle for extra relief.
I tried Assos because my good condition Pearl Izumi and Castelli shorts all got uncomfortable. They look good but the pad looses it’s mojo and then the shorts no longer work for me.
I’ve also been using Noxema as a chamois cream. (Chris Horner’s suggestion on youtube.)
I saw this too and I’m really surprised at how well it works. You need to use more than with other thicker creams, but the price is right and it works.
Lots of saddles mentioned in this thread, but no mention of the width of saddle you’re using. I found that i have fairly wide sit bones for a male, and therefore i ride saddles that are over 145mm wide, giving me a better platform for my sit bones. It also means i simply will not put a 138-140mm saddle (the industry standard, often found by default on new bikes) on my bikes.
You can try a Pro Stealth (142 or 152mm) or a Specialized Power (4 sizes from 130-168mm) or a Fizik Antares (141 or 152mm) saddle as three choices…but each of these have multiple width options.
Have you been trying to incorporate saddle width into your search for comfort? I 100% agree with those that feel like the amount of discomfort that is normal should be zero.