Actually if you just want to count the seconds (or minutes, hours etc) you are better off using time() which returns purely the seconds since 1970. From that its easier to get minutes and hours:

my $t0 = time;
sleep(61);
my $t1 = time;
my $seconds = $t1 - $t0;
my $s = $seconds % 60;
my $m = ($seconds - $s) / 60;
print ("$m minutes and $s seconds\n");
# etc