Here in the UK we’re pretty much locked down totally, popping out for easy spins but I’m not going far or fast so wanted to add an extra endurance ride (or maybe 2 of them) each week.
Problem I have is saddle comfort over an hour on the turbo, it’s fine on the road so fit is fine, how are people doing >90 minutes workouts? Is it better to do 2* 60 minutes or take 5 to stroll and stretch in the middle.
I want to get a good z2 workout since they’ll be missing for a couple months it looks like.
You just need to get OOTS regularly. I also think people don’t always factor in how mental fatigue filters down to your backside. I did 3 hours on Saturday, first hour was a mix of Z2, tempo and SS, the last 2 hours were Z2, the final 40 minutes was ok but mental fatigue was setting in.
It’s the fixed nature of the trainer/bike combo that’s the problem. Can you buy or make a rocker plate assuming your trainer is compatible with one?
Edit: It also takes time to become accustomed to the turbo, I reckoned on at least a month for the workouts in SSB. Then it takes a bit longer again to become accustomed to the 90min and 2hr workouts. You can’t just jump straight to the longer durations.
I make a note to stand every 10 minutes (unless there are really obvious circumstances that make it difficult, like doing a 12 minute interval) when using the turbo or rollers
I do the same, for every 10min ride 30sec-1min standing with very low cadence (50-60rpm) to make muscles work differently. In addition, rotate position after every standing period: upright > hoods > drops.
All these changes provide so much excitement, i don’t even need any additional entertainment 
Maybe also look at the object your front wheel is rested on. Make sure it’s not too high/low which results in saddle pointing up or down too much, compared to the neutral position the bike is in.
If you are doing a Z2 steady state ride (i.e. not an interval session), it’s more than ok to hop off and stretch or whatever for a few minutes and then continue. Your body isn’t going to go cold and reset back to zero in 5 minutes. Take a break, eat a cookie, it’s probably the least of your worries at the moment.
That, and all the bike fit suggestions. I know I fight my bike every day on the trainer but outside it’s just fine. Most likely an old injury issue. Do whatever you can/have to. 
Yep turbo versus outside rides are a different feel altogether. I spend major time on the kicker and have come to realize I need a slighly different bike fit for indoor so I have a dedicated indoor training bike (my old road bike) with a different saddle. More of a long-term solution but in the meantime you can find relief by tweaking your position for longer indoor rides for comfort. I’ve found a slightly lower and more forward saddle helps. Make sure to use premium bib shorts, stand occasionally and take 30-60 second breaks as needed to give your sit bones a break. I haven’t tried a rocker plate yet but feel it “could” help. To mix things up I’ll use my good road bike on my spare set of rollers which helps mix it up too.
I listen to Radiohead, ride Zwift and just ride without overthinking.
I stand when my bottom needs it, I often raise my front wheel with a block.
If your saddle causes you pain maybe try lowering it a little (that way it feels more weight on feets rather than on saddle).
I change my shorts half way through. Have done trainer rides up to 5/6hrs, it makes a big difference
THIS!
Gonna Amazon me a new pair right now!
I’ve done a few 3-4 hour rides on the trainer and personally don’t begrudge taking short breaks here and there- I think it makes the duration a little more manageable mentally as well. I’ve also put a folded up t-shirt under my butt out of desperation, but I don’t know if that’s recommended.
Same here. Do the longer efforts and when needed just get off the bike to stretch. While adding motion helps, I’ve done that with my Kickr direct-drive and still need to get off the bike on longer workouts.