There's two main problems, that I can see:

1. You're splitting the input on ";", but your input doesn't contain any!

2. You're taking two times, formatted like "09:50" and subtracting one from the other, presumably to get their difference in minutes. Perl won't do that for you automatically, so use a funtion something like

   sub time2mins {
     my $time = shift;
     my $mins = '';
     $mins = $1 * 60 + $2
       if $time =~ /(\d\d):(\d\d)/;
     return $mins;
   }
   [download]

   To convert before you subtract.

updated: Need more tea