Do I need a letter from my employer for my parents' Non-O visa application in Thailand?

what count down are you talking about?

I believe Tod has suggested a SETV for your parents because it is a valid visa for your parent's visit and the requirements are simpler and quicker to meet than a Non O. With a SETV there are several countdowns to consider. The Visa is valid for 90 days - i.e. gives the holder the chance to enter Thailand in any of those 90 days. I don't think this will be any problem if I understand your situation correctly. When the Visa is used by entering Thailand the holder will be given a 60 permit of stay calculated from the entry date. Sometime before the end of the permit to stay your family members could visit a local immigration office for a 30 day extension for 1900 baht each. You do not have to wait until the last day of the initial permit to stay in order to apply for the extension but \I understand there is some variability among offices about how early you can do it. You could call them to find out the rules or if you post your location here, Tod might be able to tell you. In any case the 30 days will be added to the end date of the initial permit to stay.

@Ronald *********

no a Non-O visa would get them stamped in for 90 days NOT 60 days like a tourist visa.

@Ronald *********

so you are still on your first 90 day stamp of your original Non-B visa (y)

If they applied for a Non-O visa at the thai consulate in their country BEFORE they came here they'd get a single entry 90 day one. It would be valid for 90 days <- meaning they would have that long to enter thailand AND they would get stamped in for 90 days.

You're correct IF they get a single entry tourist visa it's valid for 90 days <-meaning they have that long to enter thailand and get stamped in for 60 days

I would say If all they're doing is coming to visit you have them get single entry tourist visas from the thai consulate before they come here.