Using PHP's built-in DateTime class...
$objDate = DateTime::createFromFormat('H:ia d/m/Y', '9:30am 1/2/2012');
$timestamp = $objDate->getTimestamp();
...returns a Unix timestamp.
Documentation:
To add your variables, use it like so...
$objDate = DateTime::createFromFormat('H:ia d/m/Y', "$time $date");
$timestamp = $objDate->getTimestamp();
Or...
$time_date = sprintf("%s %s", $time, $date); // concatenates into a single var
$objDate = DateTime::createFromFormat('H:ia d/m/Y', $time_date);
$timestamp = $objDate->getTimestamp();
Note: Make sure that your variables conform with the following...
$time
= hh:mm (and "am" or "pm" is appended)
$date
= dd/mm/yyyy