Since you already have answers to your lazy (homework? job requirement?) question, TIMTOWTDI (but you'll need to adapt, almost trivially, to make this abort some other running program... by, for example, killing the other's PID or similar):

#! /usr/bin/perl
use 5.016;
# 1020073
# Timeout Timer w/o eval or SIG

print "How many minutes? ";
my $min = <>;
chomp $min;
my $time_remaining = ($min * 60);

sub countdown {
  my $t_left = shift;
  while ($t_left > 0) {
    sleep 1;
    --$t_left;
    say "Seconds remaining: $t_left";  #elaborate this sub if you want
+ output in min:sec format
  }
}

say countdown($time_remaining);

print "\a" x 5 . "\t\t $time_remaining countdown is finished\n";
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But see also On asking for help & How do I post a question effectively? ... and start showing some effort!