Heh, well thank you
So, I usually go out pretty late.
I tend to start doing a few laps om tuesday, figure out what car I want to use, or fgure out a setup if that is allowed, and see what time I get, or think I can get. Then I watch the top guys how they drive to see where I can improve. then do a few more laps until I feel confident in the car/track, and set a goal time I want to reach. Then I go for it on wednesday. Thing is, I more often than not find more time in the process, so my final time is usually faster than the target time I set for myself on tuesday.
All in all I'd say about 5 hours of testing, watching replays, and grinding for each TT. Sometimes more, sometimes less.
If you're looking for more stats regarding the general playerbase's performance in the TT's, I know
@NAXEHT has a pretty neat spreadsheet for that.