If you know the volume of your cooker then you can calculate pretty closely how much power you need to get it up to temp. It comes out to about 2.42W to raise 1 gallon of water 1 degree F in 1 hour. Your tank will cool off of course but bringing it up to temp is where you'll use the most power.
What if I changed my power to a percent and then took 10 secs and divided it by that percentage. So if it was 50% I would leave the heater on for 5 secs and off for 5 secs? 70% would be on 7 secs off 3 secs.
Only someone from Clinton would do something like that ;). If you have any temperature reading of the water then the PID library is pretty straightforward to use to help you control the heater on/off. A DS18B20 probe in a stainless steel housing (~$10) is commonly used for water temperature sensing.