For cyclocross, I've done a session like this (after a warm up obviously)
10 seconds all out
10 seconds easy
20 seconds all out
20 seconds easy
30 seconds all out
30 seconds reasy
40 seconds all out
40 seconds easy
50 seconds all out
50 seconds easy
40 seconds all out
40 seconds easy
30 seconds all out
30 seconds easy
20 seconds all out
20 seconds easy
10 seconds all out
10 seconds easy
If you are looking for maximal power, you need to make sure you are fully recovered between each rep, and i would start out at 10 seconds.
Empty the tank, then look at however long it takes to go again at the same intensity. Stop, as soon as your form fails.
Wouldn't some kind of pyramid session be best?
For cyclocross, I've done a session like this (after a warm up obviously)
10 seconds all out
10 seconds easy
20 seconds all out
20 seconds easy
30 seconds all out
30 seconds reasy
40 seconds all out
40 seconds easy
50 seconds all out
50 seconds easy
40 seconds all out
40 seconds easy
30 seconds all out
30 seconds easy
20 seconds all out
20 seconds easy
10 seconds all out
10 seconds easy