This is a fun site (look at the thermal section).
There will be a-lot of loss (additional time, maybe never) if you don't insulate.
Using the calculator, I get, with 100% efficiency, 1009 watts will bring the 10 gallons from mash-out temps to a boil in about 1 hour.
Using a 1200 watt heater, on a 120Vac 20 amp circuit with moderate amounts of insulation should be able to get 10 gallons from mash-out temp to a boil in about an hour.
I am planning an electric boil for 6 to 12 gallon boils, and plan on a 1200 watt heater. I will put some money into a ramp/soak controller and have the system dial back once it hits a rolling boil.