Not sure what you are asking here... there are no XP in WFRP3, just Advancement Points.
I usually give the group one Advancement Point each when they have completed a part of the adventure (usually about a session) and there is a natural pause in the story. They might also get Advancements based on having completed major objectives (Just to give them a bit of a meta-game incentive to work for the main goal.)
Example from my game: The characters are tasked with guarding the heir to their village throne. They are captured by dark elves. They become slaves and get involved in a big conspiracy to stage a slave uprising. After several sessions they complete the uprising and escape on a raft, but the heir dies.
They get 2 Advancement Points for all the stuff they've been through during the last sessions.
They would have gotten a third Advancement Point if the heir had survived.
They wash ashore in a village full of distrustful people from another tribe. They manage to stop some escaped slaves from robbing the village and earn the villagers trust. The village gives them supplied to last them to the next village.
They get 1 Advancement Point for having completed the village adventure and moving on. Which took one session.
Edit: And I always give Advancement Points at the beginning or end of the session. There is allways a bit of bookkeeping involved in advancment points, so I prefer to not break up the game by handing them out mid-play.
Edited by Ralzar, 31 March 2014 - 07:40 AM.