Half a day is enough
How the day stops: Bang Krachao is only half a day. Leave from Khlong Toei or Wongwian Yai, confirm the return boat before you hire; ride one stretch, one shade stop, boat back, and close at Benjakitti's lake if it meets you. Boat and hire follow the pier that day. Do not add Ancient City, do not chase the palace ticket deadline, and do not put Chatuchak on the same day.