Can I apply for a 30-day extension of my tourist visa on the day after it expires without incurring an overstay fine?

Go before it expires.

Why not go on Friday?

>Am I right that I can go to immigration on Monday 24th to apply for my 30 days extension of stay without having to pay an overstay fine

Correct

>I've read that I will get an overstay stamp in my passport anyway , that's correct ?

Correct

>s such a stamp likely to cause any problem with future applications for a new visa or extensions ?

You will not have any problems with future applications for a new visa or extension with that overstay stamp (to my knowledge).

There is NO benefit for you to wait until Monday to apply for the 30 day extension of stay based on tourism. This extension of stay is added to your existing stamp.