Yes, the restriction is applied at midnight, that is 00:00 on the specified day. There is probably no foolproof workaround. You can add javascript to the instance to prevent editing but javascript can be turned off on the client side.
Submit a tracker request for future versions. Afaict it is not likely to be changed in released versions as it is not necessarily a bug.
At any rate, it seems like a fairly easy fix which you can try to apply to your installation. Basically, change the date_selector in the module settings form to date_time_selector.
So, in mod/data/mod_form.php around line 29, change
$mform->addElement('date_selector', 'timeavailablefrom', get_string('availablefromdate', 'data'), array('optional'=>true));
$mform->addElement('date_selector', 'timeavailableto', get_string('availabletodate', 'data'), array('optional'=>true));
$mform->addElement('date_selector', 'timeviewfrom', get_string('viewfromdate', 'data'), array('optional'=>true));
$mform->addElement('date_selector', 'timeviewto', get_string('viewtodate', 'data'), array('optional'=>true));
to
$mform->addElement('date_time_selector', 'timeavailablefrom', get_string('availablefromdate', 'data'), array('optional'=>true));
$mform->addElement('date_time_selector', 'timeavailableto', get_string('availabletodate', 'data'), array('optional'=>true));
$mform->addElement('date_time_selector', 'timeviewfrom', get_string('viewfromdate', 'data'), array('optional'=>true));
$mform->addElement('date_time_selector', 'timeviewto', get_string('viewtodate', 'data'), array('optional'=>true));
hth