The heat mat doesn't really change anything. I have one under the tank merely to evaporate excess water. When i turn it off, the temp doesn't change. I do however have a 50 watt night glo that i keep on 24 hours. As long as your temp is 80-85 degrees in the day and 70-75 at night then your good!
P.S: consider getting two whites. If you have a big enough tank that is. Its so cute when they sit
together!