Making content available to a user after certain amount of time
I yes I think this is possible using Rules and Rules Scheduler

Unpublishing Content

You should check out this tutorial  (its also for Drupal 6)

Publish content exactly 24 hours after it was created

What you have to pay attention to is just do the opposite. So in the action you say Unpublish. And then of course you pick the dates. 

Hope it helps