Your body position and the bike’s aerodynamics play a big role in time trials. A couple a years ago I read a comparing of different body positions and what influence it had on the finishing time in a 40k time trial.
I am not sure, but I think I saw these results back in 1997, so this is not breaking news, rather nostalgic news.
Aerodynamics is important in time trials
An interesting question is how much time you can save by using expensive aero wheels, an aero frame or saving some pounds? There are probably more precise answers to these questions than this report calculates for you, but it gives you an idea of what difference these changes can give you.
One of the interesting findings is that slower riders will benefit more from a lighter bike than top riders will, while aero wheels and frames will give the biggest advantage to faster riders. This is probably because the aerodynamic drag requires a relative larger percentile of the workload at high speeds.
Optimized aerodynamics is better than weight savings
The conclusion for this report is that the biggest changes in aerodynamic drag and in cycling performance come from changes in body position. A more aerodynamic body position can improve your 40k time trial by over 6 minutes (that is really something!)
The report also concludes that improving the bike’s aerodynamics is more important than weight savings. A pair of aero wheels can reduce you 40k time trial time with 1 or 2 minutes.
Read the report about cycling aerodynamics