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.
30% profit is not bad if you invested a lot of money in altcoins. And what if the investment was about a hundred of dollars? is there any reason then to sell the cryptocurrency? Here, you should better reinvest.