How can I set limited time in activity?

Hello, My project is about a restaurant process, the customers have to order via application and go picking up their orders in front a store. I would like to know how I can set limited picking up times to be shown for the customers to select.

For example, my business rule is that when the customers order at 1 pm and their pickup time must be at least 30 minutes after their current ordered time, which is = 1 pm., then the pick up time must be after 1.30 pm onward.

Thank you.