I believe it says in one of the core rulebooks that the normal rate of advancement is one level for every three encounters.
No rulebook said that.
It's 1 level for every 10 encounters. Which on average probably amounts to 3-4 sessions, depending on length and amount of roleplay
We've played 25 x 4 hour sessions and the PC's just hit 5th level this weekend.
I should have offered a bit more context, my apologies.Using regular XP rules? That's about once per 6 sessions.
It sounds like every 2-4 sessions is typical, or slightly slower than the DMG indicates
What I do as a DM is get together the level's treasure parcels and make sure to hand them out appropriately. After I've handed out all of the treasure, I know I'm free to level them. So I basically level the characters at speed of plot making sure that I don't mess up game balance along the way.
We do the same thing.I saw no reason to track XP in 4e so I just level them once ever three sessions.