Every story is different. 

Some Adv RPs get great posts fairly frequently, which amazes me. 

And some post just as great posts but at a slower pace, which is understandable.

Some players and plots need the fast pace while others don't. It depends on the point everyone is at in the RP, as well as personal free time.

Generally I ask for once post a week in the IC which I don't think is asking a lot in most cases where school or holidays aren't pressing matters. In this case, I also try to stress that the OOC be a bit more active. But again, each RP is different and should be viewed as such. If posts do take longer to appear, it's more reassuring to have the OOC active to explain delays or plot, but as a GM, you have every right to ask for more quick replies if you think things are moving too slowly, or to re-assess the plot and make it more engaging, if that's an issue with the players. Overall, I think healthy communication with players involved will set the pace for posts. Ask them about their posting habits and real life responsibilities so that you can adjust expectations accordingly. 

Posting should feel like a hobby and not like a chore, if writers are happy, it tends to show in their writing. 

But you're the GM and it's your job to make the RP enjoyable but also progress within reason. Each RP has its own sweet spot and it can change with the dynamics of the writers and characters. 

In other words, just talk to your players and get a feel for what you think they can do and what you'd hope to have happen in the progression, as long as people talk and express ideas, things should progress naturally. Everyone should be happy and all that jazz.