Yes 100%.
I tried it with a few milliseconds before without any luck.
But your suggestion let me raise it up a bit. It turns out that before 6 seconds (until wifi is connected, pool is selceted etc) nothing happens.
I was able to get the connection with more than 8 seconds and not all Arduinos at once.
randomSeed(analogRead(0));
delay(8000+random(2000,3000)+random(2000,3000));
I tried delay(random 8000,12000); but for unknown reason they tried to connect all at the same time.... I know that random isn't that random but without randomSeed(); it should work but didn't.
Well now it does and I appreciate your support! THANK you!
I will tinker a bit with the delay times but for now I'm having enough of usb cables that have to be used 10 times for one sketch 