I'm pretty sure that only applies to those on 30 day visa exempt stamps. I was caught by that once and, if I remember correctly, there was an additional charge of 700 odd Baht if you were exiting Thailand less than 3 or 5 days before the 30 day permitted to stay stamp expired.
Those on "proper" visas - Tourist, Non O or Non B - shouldn't have this problem. You can exit on the exact date without the extra charge.
The Andaman Club/casino is well nice. The time I went, I stayed clear of the slot machines and just had a few beers. Their web site is here for those who might like to stay overnight:
http://www.andamanclub.com/