I'm writing a program that essentially simulates a game of tag. I want users to be able to tag another user, giving the tagged user 24 hours to tag back. If after 24 hours the tagged user has not responded they lose the game. What is the best way to implement a system that will check if 24 hours have passed without user interaction being a requirement? I believe this scenario is very similar to how Snapchat has implemented 'streaks' where users can have a streak if they each snap each other every day for more than 3 days in a row etc. If a user does not send a snap within 24 hours the streak expires automatically.

I am using .net and entity framework core with plans to use an in-memory database to begin with. Any design ideas/code snippets are welcome.