When I'm a player, 60-90 minutes between sessions is the norm for me. If it's a rule system I'm already familiar with, I spend less time on rules-research and more time on character background. If I'm not familiar with it, I do the reverse.
Helping the DM (or host) out may skew that time one way or the other. I've had DMs ask me to help out other players with a specific issue, come up with NPCs or inventive (cursed) magic items, and the like.
If all the players are on the same message board, or have email, and actively communicate/plan with each other, the time spent on character work between sessions can easily climb into the 3+ hours range.
I'm assuming you're not including social, non-game-related, events like cookouts, movies, concerts, or the like.