Try this... Although this code can break easily.

#!/usr/bin/perl

use strict;

my $t1 = "1245";
my $t2 = "0150";

Get_Time_Diff( $t1, $t2 );

sub Get_Time_Diff {
    my @times = @_;
    for my $i (0 .. $#times) {
        $times[$i] += 1200 if ( $times[$i] < '1200' );

        $times[$i] = substr( $times[$i], 0, 2 ) * 60
                   + substr( $times[$i], 2, 4 );
    }
    my $diff = $times[1] - $times[0];

    print "Time difference is: $diff \n";
}
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