The timer 'After 600 seconds' is still active even though you close the door before that timer ends. So it'll turn on 'Deur marker' after 600 seconds regardless and when it does, the second blockly is triggered because of the condition 'and Deur marker = On'
If you want to do it in Blockly then you should disable the notification on the switch 'Deur marker' (you will need this switch though because Domoticz/Blockly won't trigger on variables correctly) and make it into one blockly to prevent this so you'll get something like this:
I've tested this and it seems to work just fine (you should change the 10 seconds to your desired delay).
I get a notification after the given time that the door is opened too long, I don't get one when I close it before the timer/delay ends and I do get one again after it's closed after being open too long (so not every close of the door as you'd get with a notification on the switch itself)