They will interview the witnesses, check out the bathroom, look at area, ask questions like how long you been in Thailand, how long here etc. I remember mine is it lasted 20 minutes max. Offer drinks and snacks, maybe some lunch money.
they gave us a date at the immigration office, on the day they phone up and we meet them at the market as I am sure they were asking people if I lived in the area. That was over three years ago.