I am hoping someone can help me with this question. I have booked to do Chase the Sun next year, 205 miles with 8600 ft of elevation. I have picked the Grand Fondo training plan, with 3 workouts, one easy and one endurance ride. I have looked at the future plan and TR doesn’t increase the duration, but I am planning on doing this myself and all my endurance rides will be outside. My last experience with TR was in 2021 to 2022 where I used the time trial plan. I didn’t end up doing any time trials, but I did Ride London and I far exceeded my anticipated pace, and felt I could do it all again at the end. I have just been listening to a podcast where it recommends for the event your pace should be 60% of your hours power. This tells me that the success is going to lie in increasing my FTP. If I am going to build the endurance distance myself outside of TR, should I be doing a time trail plan again that will focus on building my FTP, or will I make the same gains with the Grand Fondo plan?
Best of luck, it’s a great ride!
I trained for this a few times. I think my best experience was with gran fondo, but I would highly recommend building in some much longer rides.
As a minimum, I would suggest a 5 hour ride once a month, kinda starting now! So 3 hours in November, then 4 hours in December and then another 4 in January and then 5 in February etc. I found this really valuable as time in saddle to find out that what was comfortable for 2 hours was agony by 4. So strengthening my core and getting my nutrition correct etc.
So I suppose pick any plan you think will work for you for longer efforts, but make sure you get some longer rides in. Zwift had a great ride on a Saturday lunchtime called BMTR I think, which was good for mileage when it’s too cold and wet to get outside.
Enjoy!
Welcome to the forum and good question! 
I’m on board with @Pipipi on this one (great response @Pipipi 
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I’d also recommend Gran Fondo as that’s probably the best discipline for really long events.
You’re going to increase your FTP regardless of which plan you choose. The differences between them is mostly the specificity of your fitness. While our TT plan will set you up to be really, really good at long threshold efforts, the Gran Fondo plan will build you up to have more diversity in your fitness, which will likely be useful out on the Chase the Sun course.
Best of luck with your training! Don’t hesitate to reach out if you have any questions along the way! 