On a normal hit(1h, 2h) strike and strike2 animations are called. They got a duration of about 0.5 to 0.6s depending on hit location. They are the same as in Native and can be checked with the Native MS in the animations.py. On a polearm hit there is a 50% chance that strike3 are called instead and they got a duration of 0.8 to 1s. The code says that polearms with the knockdown flag never call the strike3 animation.
Just tested it with Okin and confirmed it. Staffs (with kd flag) never trigger the long stagger, polearms without (like spears) do.