You must calculate your capital on that coin first, for example now the price has given you profit 30 % from your capital, i think that is good time to sell your coins. If you want more profit, you may wait for few days again. But, remember that the price can be bubbled anytime, try to satisfy with less of profit and not to be greedy.
I think you must know it first if you can earn profit, before you decide to sell your coins. If you are in doubt just wait for the another chance, maybe the price will good on the other days. Because there's is possibility that the price will recover or rise immediately, then its the time to sell your coins.