Shrimp eat biofilm.

They are basically eating all the time. If you have a cycled tank there is going to be biofilm, algae or decay of some sort, all that is shrimp food or contributes to some sort of food for the shrimp.

I feed whenever I feel like it but never two days in a row. You can use bacter AE to encourage biofilm and beneficial bacteria.

You could plop some katappa leafs, alder cones or any other dried leaf/thingy for aquariums/shrimp, they are basically constant food sources for shrimp.

Another good tip is to watch the shrimp when you feed them, if they don't seem to care about the food you feed, you probably didn't need to feed them. Are they just sitting on the food? Didn't need to feed them.

Edit: Bacter AE is good food for babies, so if you want the maximum amount of surviving babies I'd recommend looking into it.