Apparently the event is popular enough among the chain's fans that reservations fill up pretty fast.
If you're looking to do something inexpensive or light-hearted for V-Day (or are a super huge fan of White Castle), I can see the appeal.
Hour vary by location and reservations are required.
You can get a list of participating locations and more details on the White Castle's Facebook page here. The event runs from 5pm to 8pm at most locations and you have to call to make reservations.