About three hours flying time. Stay near Siam/Sukhumvit for easy BTS access.
Day 1 — River & temples
Grand Palace / Wat Pho, then Wat Arun at sunset.
Day 2 — Malls or Ayutthaya
Siam air-con shopping, or a day trip to Ayutthaya.
Day 3 — Buffer & fly
Allow traffic time to BKK (aim for 3 hours before departure).