Speaking from what I have read on these boards, some do water 1/2 thru the dark/12 and some don't.
I'm sure you will get a bunch of different opinions.
it will depend on how the plants are thriving and the system they are in. what kind of hydro system are you running? drip feed? ebb/flow? what type of medium?
some mediums dry out sooner than others, even in the night cycle. this would make sense for the grower to water sometime during the night so that they do not get stressed. thing is, during the night there is little to no heat depending on your climate and ambient temps. over watering during this time could be trouble, so water carefully. see what your plants are needing, and adjust accordingly. perhaps a small watering is all that is needed, or none at all.
its how your system is set up, and how your plants overall health is. there is no one right answer.
have you started already and notice something? or are you just trying to figure things out before you start? your plants will tell you what they need, always listen to them. with hydro make sure there is enough available oxygen for the roots to thrive also. don't over water or under water, we expect you to get it perfect! haha j/k
If your plants are thirsty looking and the tray is dry where the roots are when the lights cut on then yes. I water twice in the dark but then again it is pretty dry where i am at right now.
I ebb n flow in coco. I don't like to feed my girls when the are sleeping.
I used to feed them 1x while dark but coco does better whe it is on the drier side.