Dwight,
It takes about 40-45 minutes to bring 6 gallons of sap at 40° to a nice boil. The nice thing is that it starts to steam at about 120° so I know I'm already making syrup! Watching the aggressive boil in a shallow pan is both fascinating and terrifying at the same time. The first time I saw it I really wished I didn't have to run so far to unplug it.