If there are changes in your route, make sure you always have enough time to walk from one platform to the other and never forget the possibility of delay that could make you miss the second train.
When travelling on such short distances, you can take into account also busses and carpooling options: with some luck you will find very cheap options, even if you book on short notice.
What are the departure and arrival stations in Mae Tha and Chiang Mai?
You can take the train to Chiang Mai at Sala Mae Tha or Mae Tha, which arrives at Chiang Mai.
How long will it take you from Mae Tha to Chiang Mai by train and when do the trains leave?
The first train to Chiang Mai leaves at 12:05, whereas the last one at 13:05. On average, the journey lasts 1 hour and 30 minutes, but with the fastest connections you will be in Chiang Mai in 44 minutes.