Dunno about their hours of opening..? But when I cycle by around 11.30 each day the car-park is FULL..
..now I may be wrong here, but IMO the Dan-Singkhon Immigration crossing below P.K.K. is never gonna open to Farang needing stamps etc, when the HH office is creaming
so much Baht off us all for various visas etc on a daily basis..?? This place is a small gold mine to them.
Be warned that lunch time is 12 'til 1, although this extends according to the pre-lunch queue i.e. a lot of people waiting could see them closing the ticket machine 30 minutes or longer before 12.