I just tested and both of these worked fine for me. Note: for year, you need yyyy in small case.
Command: Test1: @datetime@[MMMM/d/yyyy h:mm tt] and Test2: @datetime@[MMMM / d / yyyy h : mm tt]
Response: Test1: September/13/2016 10:16 PM and Test2: September / 13 / 2016 10 : 16 PM