- with DB query fetch the values so that you get something like 
$blacklist = array('18:00','19:00') - check for time being black-listed with 
if(!in_array('18:00', $blacklist)){...} 
if you have white-listed values as array, and you don’t want to check in viewing part, then its better to use array_diff as @YaK answered
solved Print all times, except the ones in the DB [closed]