There is an opinion that altcoin should be bought when important news comes out about it, and during this time of the pump the altcoin should be sold.
That is not only case with altcoin only. Any sort of coin if you are dealing in, dont matter what is it, what properties it hold, that would be best when it comes to the highest price coming in market. So better is to sell out when prices are getting higher and higher. You have to be careful and observant every time. Go ahead, wait for the good time and then sell. Good luck to you.