Can I collect my extension stamp a day late without penalty?

Chaengwattana is rather strict with the under-consideration period. You cannot skip or change the date on your own. What you can do is contact them directly in advance to ask if you can go another day.

If they say, "no, you should go to the office on the day on your stamp", you must go on that day or you may risk losing your extension and doing the process again from scratch.