In Thailand for a eight days next year, and I figured this might be a do-able schedule:

Arrive on a Monday, stay in Bangkok until Thurs morning when we'll hop on a local train to Ayuthaya for a day trip. Then catch the sleeper train into Chiang Mai arriving Friday morning.

Hang out in Chiang Mai until Sun night, when we take the return sleeper to Bangkok, arriving Monday morning. Last minute shopping and eating, then hop on our flight out.

Any pros/cons for seeing Ayuthaya on the way up or down? Is that enough time in both major locations?