Ok, you have probably 1.5.7 and there is not this functionality, but I don't know why. You can repair it by changing code in {project_root}/administrator/components/com_booking/helpers/booking.php
Around line 568 should be this code:
$box->fromDate = $currentDay->date . ' ' . $box->fromTime;
if ($subject->night_booking)
$box->toDate = $currentDay->nextDate . ' ' . $box->toTime;
else
$box->toDate = $currentDay->date . ' ' . $box->toTime;
Modify it to (there are 2 new lines):
$box->fromDate = $currentDay->date . ' ' . $box->fromTime;
if ($subject->night_booking)
$box->toDate = $currentDay->nextDate . ' ' . $box->toTime;
else if($box->toTime == '24:00')
$box->toDate = $currentDay->nextDate . ' 00:00';
else
$box->toDate = $currentDay->date . ' ' . $box->toTime;
I tested in on our demo site and it should work for you too. You can see result
here.
PS: Let us know, that it helped you. If everything will be correct also for you, I will add this modification to our project, so you will not lose these changes after update to 1.5.8.