@And***
ok, It works like this
a tourist visa is valid for 90 days from the date you get it issued <- meaning you have that long to ENTER thailand on it
When you enter (even if it's the last day the visa is valid for) you'll get stamped in for 60 days <- the amount of time you get entering on a tourist visa,
AND
you can extend that once for 30 days at the immigration office