Change permission group based on time played?

I'm interested in setting up my permissions system so that new users have to wait awhile before they get access to several commands (creating factions, etc.). I could have sworn I had seen a plugin that would cover this, but my search-fu is lacking at the moment. Am I crazy, or is there already a plugin that will do this?

I'm using PermissionsEx currently.

Thanks,

semibreve42