Since you're not going to be able to work the current diner staff 24 hours a day, so the only way to do that is provide for a second crew so they can rotate (port and starboard is bloody miserable, but you can do it for a day or two).
Assume you can sell as much food during non-meal hours as you can during meal hours (that's a horrible assumption, you won't sell anything near that much) and congrats - you've just doubled the dining car losses (in reality you'll more than double them since you're not going to sell as much food during off hours).
Sounds like a great plan to me.