Hi
Recently there has been a debate concerning stretching use for athletes. It has not been proved it can protect against injuries or such as usually thought, the only thing is that it makes you more flexible.
Personnaly I am practicing track and field, pole vault and 100-200m distance running. I do stretch after the first a few minute of low intenisty jog, just to get in the activity. I am doing a second stretching session (usually longer than the first one) at the end of training.
on 2h of training, stretching is about 40 minutes for me.