You are approved on the basis of the credentials of the first school you buy classes from. 6-months is the minimum program. That program will consist of a certain number of classes which you will have 6 months to take. So, you can certainly train in BKK for a month, go to Phuket for a bit, but unless you can find a school with multiple locations where you can use the classes, you will have to return to BKK to continue your 6-month program.