Perhaps if you generalized the interface a bit more, and made it apply to any sort of data in a list ?

List::Aged perhaps ? or maybe List::Expires ?

Update:It occurs to me I might be clearer with an example:

use List::Aged;
my $list=List::Aged->new();
$list->add( -expires => "60 seconds", "some","list",
       "of","random","stuff");
$list->add( -expires => "10 hours", "whee");
$list->exists("random"); # true, for now
sleep(61);
$list->exists("random"); # false now
$list->exists("whee"); # true
[download]

Then again, a list would denote values that don't have to be unique. The exists() routine sort of denotes unique members. Blech.