#!/usr/bin/perl -w
use strict;
use Time::Local;

my $start = "7:30";
my $end   = "11:45";

my $interval = 15;

# Assuming time is in a 24-hour format and adjusting for my timezone :)
my ($start_sec,$end_sec) = map { /(\d+):(\d+)/;timelocal( 0, $2, $1, 1, 1,1970 ) } $start, $end;

# In case the times cross the midnight boundary
$end_sec += 86400 if ( $start_sec > $end_sec );

my $int_sec = $interval * 60;
while ( $start_sec <= $end_sec ) {
    printf "%d:%02d\n", (localtime($start_sec))[2,1];
    $start_sec += $int_sec;
}