[SOLVED] Rule cooldown

I’d like to build a rule that can only trigger once per evening.
When the outside temperature is below the inside temperature I want to receive a push notification via myopenhab but I only want to get this notification once.

Does someone know an easy way to implement this?

Bild a gloabel variable var msgSend=false and set to false every midnight.
Trigger the inside and outside temperature for changes.
Check in the then-part msgSend, the time and if outside is below inside, then set msgSend to true and sendMsg.