It'll take much longer than 2 hours to snuff it. I have this exact same smoker. The ceramic holds the heat for many hours after shut down. Even though you're starving the smoker of oxygen, the embers will remain super hot for a long time.
Next time, right before you shut it down, take a look at how much lump is left, then close all the vents for shutdown. In the morning, look at how much lump remains. You'll be surprised that it looks almost identical from when you last looked.
I've cooked butts, fresh hams and several whole chickens on mine and this thing is very frugal with the lump usage. I don't have one tiny wisp of smoke leaking anywhere. Happy smoking, shut that lid, open tomorrow and repeat!