Illwinter manual failed: the def check is actually vs 3d6+ and not 10.

The delay for trampling (in ticks) is:

max(10, 10000/combat speed) + (7500*action time)/(largest size difference in the trampled square/2 + 3)

Things that affect action time (default is 1.0) are

1. Quickness, half
2. Being frozen, double
3. Being slimed, double
4. Being slowed, double
5. Something else which I assume is heroic quickness