The bes time of selling your altcoins is the end of every year . Always in this part of the year altcoin rich ther maximum .
Cryptocurrencies are naturally volatile in price, that is why we can't predict when it will rise and when it goes down. So, for me, sell your coins when the price gets higher than the ICO price and when you think that you really can get a good profit from it. Take that big advantage.
Generally we know that any product when we buy on low price is a benefit and we sell in a high market if we want to make profit. Similarly like Bitcoin we should buy Altcoin in its low market so that we buy coins on low amount in large quantity. This is a benefit in the start and then we sell the Altcoin in its high market on high price in order to make enough or maximum profit.