Did my first TT last month. The pointer I was given by a seasoned TT'er is to follow 3 essential rules:
1) Don't start too fast;
2) Don't start too fast; and
3) At the beginning of the TT, refer to Rules 1 and 2.

As to times: You should use this first one as a benchmark. Try to manage your energy well and make notes as to warmup time, gear (bike, clothes, helmet, which gears, average rpm, etc.) and weather conditions. Do more TTs and compare notes.