Time::Local is probably what you want (presuming you don't need subsecond accuracy). This should print "10" because it sleeps for 10 seconds.

use Time::Local;
my @now = localtime();
my $epoch_time1 = timelocal(@now);
sleep 10;
@now = localtime();
$epoch_time2 = timelocal(@now);
print $epoch_time2 - $epoch_time1;
[download]

Update: perldoc -f time :-). My example is just something to play with to show the differences between the available time representations.