Subscription Mod?

[geocodes]

Hi,

I'm working on a plugin that will promote users to a usergroup based off specific requirements. The way I wanted this to work, is that they are promoted for x time, almost like a paid subscription. Is there anyway I can use the subscription manager for this without making subscriptions for each usergroup?

Oh and also, how often does the system check for expired subscriptions? When I set a subscription to end in 5 minutes after the start time, the user was not demoted. Does it only check for expired subscriptions once a day or something?

Thanks a lot for the help!

-Geo