@Seiko I choosed your approach… 4 flows
Installed the Countdown App and created 4 flows:
Gate is open:
Gate is closed:
30 minutes reminder:
60 minutes reminder:
Tomorrow the Window Washer will visit the house, let’s see how this turns out:-)
Future plans
Closing the gate automatically, therefore I started a post with an app request… no response so far… 
I should repost it here I guess
In the mean time I bought a GoGo Gate, which I can connect with IFTTT and automate it…
For now, many thanks to @seiko and @HTilburgs
