How long to hold a cryptocoin/altcoins to earn good profits?
A day or more is sure to wait for a good price increase on altcoin, but I prefer daily because altcoin is more volatile not like bitcoin, but there are also some altcoins that are suitable for long-term monthly or even yearly such as BCH or BTG.
Generally only hold the good top altcoins for a longer period or if you can find the prospect among the newly listed coin which in future can grow a long way then you can hold such coins. Rest of the coins are generally being used for the pump and dump strategy and if you gain a good % in few days then you should ideally be selling and booking your profits and move on to another coin or sell partially if you still think it has some potential to grow future.