Depends on a lot of things. How hot is the grow area? What's the humidity? What's your medium, rockwool, clay pellets, coconut fiber? With rockwool you may only have to water every other day or even less. With the prefered medium (clay pellets) you may want to water once per hour for 30 seconds. The point is you'll need to experiment to find the perfect time. Believe it or not, the goal is to have your roots as dry as possible without stressing the plants. I would keep decreasing watering times or amounts until I started noticing any stress on the plants or any one plant, then crank it up a notch.

Sorry I'm not real familiar with the wilma 4 pot, perhaps someone else could give you a better approximation based on their experience with your settup, but I tried.

In my opinion the time of the day that you water does not matter in the least. It rains at night, morning, and several other times of the day, and outdoor plants usually manage to survive, and sometimes even to thrive. I'd be happy to engage in a discussion with anyone about this, but be prepared to show me some proof. Scientific-botinological-like proof.