Coolant Heater Question

My '05 came with the coolant heater and I want to plug it in at night since it's been getting down into the 20's here at night. I looked at the manual but it really doesn't give any guidelines for plugging it in over night. Any ideas on how best to used it?

For a nice warm motor and instant heater on a cold morning.
Plug it in before you go to bed and unplug it before you want to start it in the moring.
MT

I got an aftermarket heater, and it said specifically not to leave it plugged in overnight or damage could result. I believe 5 hours was the maximum it says it can be pluged in. I have a timer hooked up to the extension cord that comes on at 1AM so it's nice and toasty at 6. Saves a lot of electricity and an extra trip outside before I go to bed.