The best time is the time you have set and you take off profit when it reach that.
Unfortunately, the price won't always reach the target. Sometimes, after buying and setting a specific price as the target to sell, the price of the coin drops constantly. Some people can feel frustrated and decide to sell immediately. Because of this, I don't want to specify a certain time as the best time to sell. In my view, when we sell our coin, should be the right selling time. The right time or best time isn't only determined by the number of profits but how important it to sell the coin at that time.