@Michelle ********
the way it works IS
IF the immigration office will let you go straight to a 60 day covid extension (some won't and make you take the regular 30 day extension first) they will start the covid extension on the date you apply for it <-meaning you will lose any days you have left on your current 60 day entry stamp
BUT
IF you take the 30 day regular extension first they start it on the day your current stamp ends. <- meaning you don't lose any days
All you can do is GO and ask the immigration office at Chaengwattana Counter J if you can get the 60 day covid extension now or if you have to take the 30 day extension first.