Songkran in Chiang Mai centers on the Old City moat and Tha Phae Gate. This guide puts Old Town routes through that area first and groups the rest by morning and afternoon; April daytime reaches 35-40 degrees.
The Old Town temple half day runs 07:30-11:10 past Tha Phae Gate, the Three Kings Monument and Wat Chedi Luang, and the EV tuk-tuk gathers at 10:00 and ends at 12:00. Both leave you easy access to the festival inside the Old City afterward.
Cycling has two slots. The classic ride is 08:00-11:00, and the combo is 14:00-18:00, crossing the Ping River and ending with a northern Thai meal. Bring a raincoat if it rains.
The costume rental near Tha Phae Gate is open 09:00-20:00 with last entry at 15:00, and costumes must be back before 20:00, so plan the photo session within the afternoon.
The Doi Suthep sunrise picks up at 05:00 and ends at 08:00, leaving the day free, and Rafting & ATV offers 08:00-16:00 or 11:30-19:00. The waterfall-park private tour picks up at 08:00 and returns at 15:00.
Pack clothes that meet temple dress rules, and check pickup surcharges for outlying hotels on each listing. Some tours have minimum numbers.