I only do time trials if I'm trying to bump up my SR a little, like Jav said.
If I am going to be serious about a race, like I was with the Lotus 79 this week, I run test sessions for the first day, just long enough to get comfortable with the track layout. Then the rest of the week is open practice, and then I wait until the SOF race comes up, and then I crash.

LOL, well the crashing part doesn't always happen, but it did this week.
Open practice is key for me, because in TT's you are still by yourself. I run side by side with people running a similar pace in open practice, this allows me to prepare myself for how side by side racing is conducted through each corner, proper passing zones, and where to get a run on people.
It's true that you don't have to be fast to finish well, just because of attrition, even in the upper series. I was running a good 2.5 seconds slower than the leaders but I was maintaining 5th place just by being moderately quick and consistent. The Lotus with the OTM and it's downforce dependent twitchy nature shot me off the track in one corner and finished my race, but had I not made that mistake, I likely would have had a top 5 just by being consistent and safe.