Using millis() for waiting after sensor activated

Projects Programming
1

I'm going to make an garage door sensor that tells me the statement of the door (closed/open) in the Blynk app. So far all ok.

If the garage door is open for more than 30 minutes, i want an reminder. I need to know how i can make my ESP32 wait for 30 minutes before sending me a notification, and after that i do not want more notifications.

How will an millis or blynk timer code look like regard to the timing?

2

You should keep all the questions about your garage door opener in one place. For one thing, the code is already there:
https://forum.arduino.cc/index.php?topic=675166.0