Is there a way to disable the cache on a template?

In my case, I need to create a splash page that displays if the site has not been viewed for X hours. My solution was to store the last accessed time in the session log, and use that to determine whether to display the splash page. The splash page is a block on the home page that has a custom template applied to it. If the user hasn't viewed the site with X hours, the template displays; otherwise it doesn't output anything.

The problem is that the block is cached, so it always displays the splash page. How can I disable the cache on a template?