Thanks... but not for me; NO reservations.
2 months old posting:
"The first Bus leaves at 5:00 a.m. From there, there is one departure every hour. Boarding is on a first-come, first-served basis. Since there are limited seats, it is better to prepare early. Departure times are quite accurate."
And;
"Typical Thai 'squeezer' minibus, 180 THB to Don Mueang. You can save yourself the trouble trying to reserve a ticket: they just don't do that there. Buses leave hourly (full hours)"