As much as they need, whenever they need it.
There is no precise volume or frequency to watering; it is all very variable and depends on things like container size, plant size & root mass, soil/media properties, and your particular environment (air flow, lighting, temperature, RH). Fresh transplants initially don't need to be watered very frequently; but this will change as roots grow.
So the proper way to water soil\less media is to water thoroughly when you do water, until you get run-off so you know the media is saturated. If you lift your pots now they will be heavy. Then you wait until the soil surface has for the most part dried out (before it is bone dry). The pots will be much lighter and easier to lift. Then you water thoroughly again.
If you wait until the soil surface is all hard, cracking and/or pulling away from the sides of the container; you waited too long*. If that is the case you'll need to start watering very slowly. There has to be some moisture in the media for it to even absorb water properly, otherwise you can end up with dry spots where roots will not grow well, and what looks like nutrient deficiencies.
*If your soil is too dry and you go to water it you are likely to notice that the water initially pools up on the soil surface. It may run down the sides of the container and out the drainage holes, apparently as run-off, but in reality very little was absorbed into the media. I see this all the time.
Dump or siphon off any run-off after 30 minutes or so, don't let the pots sit in stagnant water.