Might seem like a dumb question, but I figure I am a noob so I am allowed

Why can't the babies be fed frozen mysis that is pulverised or some other non-live food? I am guessing there is a perfectly logical answer for this one, but I was asked this and I don't actually know why. Also, how long would a tank need to be set up to be considered safe to add seahorses to and should a fish like a damsel or something just be kept there until that time, then taken out so the tank remains cycled and so forth? What is the purpose in waiting a long period in time past cycling if you have no live rock? Does the extra time make it more stable somehow or is it just to build up a copepod population?
(Sorry these questions are so nooby

and thank you so much for having the patience to answer them!)