Unfortunately there's not a simple way to do this. You can try this (I haven't tested this):
Change lib/Application/Schedule/DailyLayout.php GetLabels() function to:
public function GetLabels(Date $displayDate)
{
$labels = array();
$periods = $this->_scheduleLayout->GetLayout($displayDate);
if ($periods[0]->BeginsBefore($displayDate))
{
$labels[] = $periods[0]->Label($displayDate->GetDate());
}
else
{
$labels[] = $periods[0]->Label();
}
for ($i = 1; $i < count($periods); $i++)
{
if ($periods[$i]->IsReservable()){
$labels[] = $periods[$i]->Label();
}
}
return $labels;
}
Then lines 53-55 of tpl/schedule.tpl to:
{function name=displayUnreservable}
<!--<td colspan="{$Slot->PeriodSpan()}" class="unreservable slot"> </td>-->
{/function}