A “Tourist Visa” for Burma/Myanmar allows you to stay in the country up to 28 days and is valid for three months from the date of issue, it also allows only one entry during that period. If you find yourself in the country more than the 28 days, when you arrive at the airport to depart, customs will charge you US3 Dollars for each additional day overstay.
Once you’ve overstayed, you will need to take care of the administration and the payment. If you’re leaving from the Yangon airport, just give yourself a bit more time, check in at the counters downstairs, then head up to the second floor. There is a sign that says “immigration – overstay.” Here you’ll find the immigration office.