They will absolutely be fine between dusk and dawn without sustenance. The fact that they havent died yet indicates that it is alright.
That was actually common practice in the past. In fact, scheduled feeding can help regulate a chickens life. It encourages foraging, keeps them close to home and keeps egg laying on a regular cycle. SO it has benefits.
Chickens go to sleep at night and in my experience, they dont get up to "go potty" or "raid the icebox..." so why leave feed around for the mice or other nocturnal scroungers? However, they DO get up early, so a way to keep water available at all time should be worked out.
As to feeding, it has always been recommended that you use a triple feeding schedule .... Early morning, noon and mid afternoon.
(However, gritsar makes a good point. Early for a chicken means, "crack of dawn.")
As part of this triple schedule, add a fourth feeding of grain moistened with water or skim milk just before dusk. This is easily digested while they sleep and this "cereal snack" tides them over the night... works the same for human babies.
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Most people don't bother with all that, though, and just leave the feeder full all the time. This is very convenient for the chicken keeper, and there really is nothing wrong with it. If you don't have the room for it, so be it. The chickens aint gonna die if they dont get breakfast before 8 AM.
Something you may wish to consider is feeding outside. It is harder to keep moochers like wild birds and mice out of it, and the feed must be kept dry and protected from the elements. But, otherwise, that has been done before with good effect.
Interestingly, the "modern" recommendation to keep the feed hopper full is a direct offshoot of that most hated and despicable of all human endeavors - the commercial poultry business.
