We, in the army, had 6 hour checks that we pulled. At the same time, we fueled up the sets. That way we would never have a gen set run out of fuel, while on line. That was at least the wish and hopes.
I think, and I do not want anyone to assume I am close to right on this, but assume, mornings, (07:00) are high draw. From morning to about 17:00, you have a lower draw, (everyone is at work/school) and then from 17:00 or 18:00, until maybe 21:00 high draw, that you should get maybe, (don't nail me down on this) 8 hours run time to a fuel tank. I would still fuel up every 6 hours, if I had the chance. 8 hours is a long stretch. I simply would not feel good going that long.
The best way to alleviate that problem is to have an Aux fuel system. A 55 gal oil drum. Check it once a day. Refuel as needed. We had a different mind set in the army. If you run out of fuel, you put on a pullover, and toss another blanket on the bed. We, in theory could have some friendly communist gentleman drop bombs on our butt. We fueled every six hours.
Even if you run all night, the load will vary. A 55 gal drum would be a good idea, if you want to sleep all night. But do not forget, our 6 hour checks were not with out reason. Your baby wants you to look in every now and then. Gives you a chance to look, listen, feel and record data. Keeping a check list, with a few items of data listed on it, can tell you if, say for instance, the temp is going up. Or oil press. going down. Or battery charging ammeter is not going down as the system should be charging it up. Or the battery charging ammeter going into the red, - region. And best of all, checking oil. Is the set using oil? Is for instance the oil level going up?!! That is always bad!! Looking for leaks.
This will sound crazy, but we used to sleep on top of the gen sets. It was warm. We were near by if something happened. You can hear the set run, hear them not work right. Hear them oscillate. You do not have to do this. But 6-8 hour checks are not to be forgotten. Anyone can do them, with a little prep time. Put on some hearing protection, get some rags. Carry a clipboard. If you need oil, have it near. Checking coolant is not recommended. If the temp starts to go up, turn off the set, let it cool and then check. Hot coolant hurts. Look at the belts. When they get loose, you can see them flap in the wind. All this leads up to some key words, Preventive Checks and Services. Better known as PMCS. Its in your -12 book. Read it. Do it. You and your gen set will be happy campers!