If you don't need tight performance, I recommend that you use Date::Manip. Here's an example.

use Date::Manip; 
$limit = ParseDate("12 hours ago") or die "internal error";  
while(<>) { 
    /^(\S+).*\*PASS\*$/ and Date_Cmp($limit, ParseDate($1)) < 0 or nex
+t;   
    print "found: $_\n"; 
}
[download]

Update: I see that blue_cowdawg has dome almost the same as me.