It's much better if you reorder it. "Between 11:30 am and 1:30 pm, tables are only for customers who are eating here."

What Kris said, you're golden. "Sentence", though.

Yes, that is correct. Keep up the good work!

These tables are reserved for customers only between 11:30 and 1:30. ('customers only' is very direct and clear, people know what the message is) Thank you for your understanding.(softens that direct message)

No -- the problem is it suggests customers eating before 11:30 and after 1:30 are out of luck, whereas you probably intend to suggest it's open seating other than at lunchtime. But a comma after "here" will fix it, or perhaps more natural, Ed's suggestion.