Because advanced RPs generally involve much more complex posts than say, casual, the requirements one should have are also much more complex. As said by others above, it can be anything from very frequently to weekly or slower, all depending on the RP story. Some RPs, like one we're in, has very slow post rate because there's four active factions in it (at least), and those coordinate internally before they post. The OoC is active, as is the IRC, so its not dead even when many days go between IC posts from anyone.

In some Advanced RPs one can even go through a several-week dry spot only to have it return to full activity later. But that's generally proportional to length of posts. Longer posts = wider gaps between posts permissible without danger.

The best system we've found is to have some means of OoC activity even when IC is dry. We're personally quite fond of the IRC, as that allows more direct contact than the OoC tab, but we will also use that, as it allows records in a way that IRC does not (without someone posting logs, that is)