I have successfully implemented a countdown timer incl. auto-advancing on the block level thanks to this support:
https://qualtrics.com/community/discussion/comment/20771#Comment_20771

However, I recognized that a new timer appears (which indicates more time left) when the respondent uses the back button or has to correct his entry after an error message:

!

Is there a way to fix that problem?

I thank you so much in advance.