When Mark Cavendish says he's sprints at 1500 watts how long is that for? In an interview with Cycle Sport, Cavendish said he puts out over 1500 watts of power.


  “You’d be surprised at my watts,” Cavendish says.
  
  “Most people who say that their maximum is 1,600 watts won’t put out
  1,600. My maximum is 1,580, and that is a lot. Not many guys will do
  more than a hundred more than that. But no one will ever get close to
  that in a race after 200 kilometres,” he continues.
  
  “I put out 1,490 today in training, on bad form, but I won’t put that
  out in a race. It’s not watts, and it’s not just my frontal area in a
  sprint. It’s everything beforehand. How I ride in the peloton. My
  pedalling action. How I sit. I save so much energy for the finish.”


Is it 5 second power or 30 second power?
That kind of power is going to be between 5-30 seconds, and is most likely a 5 second maximum, or he's quoting the absolute peak that he put out.

There is a very interesting analysis of several Team Columbia riders from a couple years ago when Cavendish won the stage. A few riders have 30-40 second pulls at the front in the 650-700 watt range, and in the leadout, Markus is at 700+ watts for over 30 seconds with a peak over 1000.

So if the leadout is at 1000, Cavendish probably is doing 5-20 seconds in the 1200 range as he comes around the slingshot, with surge peaks into the 1400 range, but that level is not sustainable. You can see this when sprinters mistime their sprints and start losing steam short of the line.

Here is the link with the powerfiles.