Anytime is the right time to buy alt coin, because if you think about it you should have bought a coin already when it was still on its lowest price, imagine buying a coin for a larger amount yielding only a small amount. You should do an extensive research about marketing, financing, and the alt coin that you want to invest in, by saying that you should buy an alt coin when it is in green light is a bad move but it is still up to you whether you want that small profit or not.