It's like any foods and safety measures. I'm not certified in food safety but there are temperatures that make food safe. Either refrigerate it to keep it under 40 deg F, or keep it heated over 140 deg F overnight. If you have a cooler, you can put the tomatoes in it with lots of ice to keep it cold overnight.
I'll be starting a big electric 18 qt roaster batch of tomatoes tonight, so I'll bring it up to temperature to boiling with the lid on, then leave the lid cocked at a right angle, so half of it is on and half is off to allow evaporation. I'll keep the temperature above 140 deg F, usually steaming hot, more like 170-190 deg F overnight. Then in the morning I'll stir and bring the temperature up to boiling again and keep cooking it until I have about 10-12 qts left, then can a fairly thick sauce.
Under 40 deg F or over 140 deg F.
