Change day's starting hour [building TV schedule]

go to calendar.module at line 418

function calendar_groupby_times($type = '') {
  $times = array();
  switch ($type) {
    case 'hour':
      for ($i = 0; $i <= 23; $i++) {
        $times[] = date_pad($i) . ':00:00';
      }
      break;
    case 'half':
      for ($i = 0; $i <= 23; $i++) {
        $times[] = date_pad($i) . ':00:00';
        $times[] = date_pad($i) . ':30:00';
      }
      break;
    default:
      break;
  }
  return $times;
}

and change that $i value " for ($i = 6; $i <= 23; $i++) " in your case

The D6 branch is no longer supported so we're closing this issue. If you think this issue still exists in D7 you can open a new one.