how long depends on the one you buy

there are different ones, electric ones and diesel fuelled ones. the diesel ones ideal for vans/off roaders who dont want to be tied to a plug.

for home use the electric ones are fine. They say its about 30-40 mins if you include interior. They have a simple plug you hide in a grill/hole somewhere so no complex wiring each day.

Easy way to use it is to set it up on a timer plug in the house, that way no need to remember in the mornings.