have no exactly time when to trade, you have to follow news, events daily and study technical tools RSI, Bollinger bands...to sell and buy to get profit, and one more impotant note you need to know NOW market are uptrend, downtrend or sideway to target profit ( 1%, 5% ...)
For me, knowing how to read the market chart is as important as knowing when it is dump or pump. When it comes to trading, it is very important to sell high and buy low to ensure profit but it is hard when you are already. Dealing and watching the fluctuations and it is very stressful when you see that the coins you are trying to sell are going down most of the time. There is no best time to trade because no one knows when is the "best time" really. We traders always make speculations and assumptions of a good price for us to sell our coins.