Comparing post date versus datetimestamp

[lionheart53]

I'm trying to have my search results show older posts differently based on the user group. I've got a calculated date using something like below:

$startpostdate = time() - (90 * 24 * 60 * 60);

I then in the search results want to compare it versus the date/time of the post (which i assume I use $post[postdate]). But $post[postdate] is a text format and I tried using strtotime with no results.

Any thoughts? I'm sure it's something basic I'm missing. Thanks