Do I need a time counter if there is NO serial for lets say 20 seconds?
This sounds like a job for millis() timing so that the input can be checked for a period.
Have a look at url=Using millis() for timing. A beginners guide - Introductory Tutorials - Arduino Forum]Using millis() for timing. A beginners guide[/url], Several things at the same time and look at the BlinkWithoutDelay example in the IDE.