Its time to sell your altcoins when you are in profit. Any percentage as long as you are in profit minus the charges is a good time to sell. Buy back again at lower price and sell again at a higher price for a profit and do it again and again. The major aim trading is t save your capital and gain profit.
As I have said this strategy is very simple and good but you can put it into practice only if you're an experienced trader with strong nerves, and the market regularly gives waves of different sizes. Now, in the falling market, it's hard to work with this strategy!