I got my first chicks about 6 weeks ago, and I'm a little embarrassed to admit that a few times I 've snuck out of the house and went out to the workshop to check on my little babies in the brooder well past midnight.
What I found was that the little babies under the heat lamp were usaually fast asleep, but they don't stay that way all night. they are constanly waking up and eating and drinking and pooping and then going back to sleep. The funny thing is they almost never do anything individually. when one wakes up, they all wake up. When one pecks at something they all run over there and peck at it. When one gets hungry and eats they all suddenly decide it's dinnertime. And when one gets a drink, they all decide that's a good idea too. I'm thinking of cancelling my direct TV because I spend so much time watching chickens now.
I installed overhead lights in the large aviary where the older birds are and I find that If I leave the light on, they too will wake periodically and eat and drink throughout the night. I'm not sure what they do with the lights off.
But the younger chicks seem to not know the difference between day and night especially if they have the heat lamp on them, so they going about there eat, drink, poop, sleep, eat, drink...routine 24/7.
I keep food and water with them all 24/7., But that's just me.
I think the question would have to be is there any harm in keeping food and water with them all the time.