What are you forcing? And what clicks? What does a warm up need to achieve? The increase in oxygen uptake cited above was achieved with 15 minutes at a very easy pace, which makes me wonder if a harder warm up could be considerably shorter. And I agree with Boardman, that there's significant risk of tiring with an extended warm up.

While I'm familiar with "the shorter the event, the longer the warm up," it sounds more like tradition than science to me. I also know a good number of masters racers who basically say "from the car to the start," and I'm not sure that's any less valid.