Yeah. If the poster really means VOA and not Visa Exempt then possibly that can take some time. So if that were the case and they are slow then the minimum would be 1.5-2 hours of them waiting landside.

Assuming that they are heading to a hotel in BKK, really the best thing would be to have the hotel arrange transfer to the hotel and let them relax in the hotel while waiting for the OP to arrive. It would certainly be easier for them to find the door with all the hotel greeters and then be taken care of by them, rather than go upstairs and sit in one of the crowded restaurants. If they have enough mobility to make it from the plane to the restaurants, having the hotel greeter put them in the hotel car and send them to be greeting at the lobby and checked-in should be a breeze.