Day 1: walls and the river
Day 1 is only the walls and the river. Tha Chang into the Grand Palace and Wat Phra Kaew: the ticket page says daily 08:30–16:30, sales until 15:30, 500 baht for foreigners. Walk out and buy Wat Pho's separate 300-baht ticket (08:00–19:30). If dusk remains, the short ferry at Tha Tien to Wat Arun, one terrace, then stop. Do not add Khaosan, Chatuchak or Thonglor.
Day 2: one main mall
Day 2 keeps one mall as the main hall. Go deep in Paragon and insert an hour at Jim Thompson (daily 10:00–17:00, adults 250 baht, guided house); or switch to the Ratchaprasong skywalk and Erawan, in which case Pratunam is a different kind of buying, not more luxury. Lumphini can be dawn. Do not add Thonglor or ICON.
Day 3: market or lanes
Day 3 goes to Chatuchak only at the weekend: Or Tor Kor first, then one direction, and the park when it is hot. The TAT Japanese page lists Saturday and Sunday 09:00–18:00; weekdays are partial, so follow the gate. On a weekday, take Thonglor in the evening or Ari's lanes. Ancient City replaces the whole day; it is not an evening add-on. Do not return to the palace.