It greatly depends on the amount of people. I finished 37th out of 614 on Party once and took a little under 3 hours. I would imagine that the final 2-3 tables would take another hour or 2.

EDIT: also you will find with freerolls that in the first 20 minutes of the tournament dozens of people go out in one way or another. My theory is that people register way ahead of time and simply forget because it's not really money out of their pocket. So plan on your first table being very slow in the beginning.