The answers to all of those questions depend upon the game speed that you have set. The faster the speed setting, the faster the fishies grow, and the faster that they will become hungry. Also, the level of Food Research that you have completed and certain things that you can buy for your tanks will affect how often your fish get hungry.

It takes about 2 hours for babies to grow into adults on the fastest speed. I generally set my game speed to the slowest speed overnight, since I can breed the fish at bedtime and the babies will be pretty much grown in the morning. Since I won't be doing anything with the game while I'm asleep, it doesn't make any sense to run it at a faster speed.