How many watt is your heater? They come in different sizes, and the big ones need to be on a lot less time than the small ones.
All night will guarantee everything is as warm as its gonna get... but a big heater can heat a 4020 in a few hours.
If you do not want to waste electricity, you may want to invest in a timer that will turn the heater on at say 5am. I use several of these, and for the most part they work well.