How long do you leave printed material on printer(post heat area)?

Our machines (Epson/Roland) will turn off the heaters once a the last job has finished and the machine has sat idle for 15 minutes.
Check if the Mimaki has a power save setting which can also do this.

 

I wouldnt recommend leaving it on idle every night, but if it's once in a while it should be fine. Our JV33 lasted about 7 years (we ran average 3-6 hours/day) and then put it in sleep mode at the end of the day (never completely shut them off or unplug as they have automatic cleaning cycles). Sometimes if the power went out from a storm it would be on in the morning, but other than having to soak the head sometimes (more towards the end of its life) and wasting electricity with the heaters on, it was fine. I dont remember the JV33s having many power save functions, but our CJV-150 & JV-150 are set up to go to sleep after a 1/2 hour of not running (it sometimes takes longer than that to rip a big/complex design before it shuts off )