Whenever you accept a flirt request, or someone accepts yours, a 24 hour timer starts. Within this period, you need to decide if you want to match or, if more time is needed, extend the timer. Both you and the other flirt must agree to match or extend for the timer to stop or reset.
To match or extend, open the chat with your flirt, tap the plus icon in the bottom left corner, and choose either ‘Match’ or ‘Extend’.