Personally, I like to have more time than necessarry and would choose 9 or 9:15 if available. There is so much to see and do at TT after the ride itself that if you have a little extra time to spare it won't be wasted.
NOTE: Last week we arrived at out fastpass+ time to be taken aback at just how many others were in the fastpass return. We walked over to Mousegears for five minutes or so and the line disappeared. With the new system it seems to take a bit longer to initially get those lines moving as you have to use your band to get the Mickey to turn green on the fastpass post instead of just handing them a paper pass.