Erm, given start and end as time_t values (use Date::Parse or whatever to get them there) just convert your interval into seconds and add.

sub intervals {
  my( $start, $end, $interval ) = @_;

  my @ret;
  my $cur = $start;
  while( $cur <= $end ) {
    push @ret, $cur;
    $cur += $interval;
  }
  return @ret
}
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