You can enclose the check for time conditional within a repeat that is canceled when the door sensor is in the closed position.
Edit: So this way, even if you open the door at 4:30, have the repeat occur every 15 minutes, the door opening at 4:30 will trigger an action that occurs at 9:00 pm.
Ok I like this! Especially because my next step was to allow it to be open for a period of time without warning (even if I open it after 9pm to take out the garbage or something)
So if I check every x-minutes, I'll set a boolean (GracePediod = True or something) and upon next check if it sees grace period was true, THEN it alerts.
Will try this out tomorrow, thanks to both of you!