([0-2][0-9]|(3)[0-1])(-)(((0)[0-9])|((1)[0-2]))(-)\d{4} (1[0-2]|0?[1-9]):[0-5][0-9] (AM|PM)
Example
<input type="text" class="form-control" value="" placeholder="Pick a datetime, e.g., 21-02-1952 12:59 PM" pattern="([0-2][0-9]|(3)[0-1])(-)(((0)[0-9])|((1)[0-2]))(-)\d{4} (1[0-2]|0?[1-9]):[0-5][0-9] (AM|PM)">