The current Bitcoin market is going through a period of volatility, only the right and suitable ideal investors can use this dip. It is best to use the dip along with buying Bitcoin according to the DCA method, because this is the best time to hold Bitcoin.
Bitcoin has always been subject to volatility, it not just the current state of Bitcoin although we have some time when the volatility sharply increases than normal and sometimes become less but it still doesn't change the fact that Bitcoin is a very volatile coin..
Also, there's no best time to hold just "HODL", buy DIPs and continue your accumulation strategy preferable DCA... with DCA buying of DIPs is pretty much covered although here could be sometimes you might want to catch a dip before it changes direction.
A long-term holder should never think about selling his holdings.
it's not that they should never sell their holdings, they can sell at some point, not selling all (but in small chunks as profit when the time comes and they've accumulated enough to start doing, JJG has a thread dedicated for it ) yet we shouldn't be discussing "how" as most of us here and people visiting the thread are still in their accumulation stage so it's just better to focus on the point "HOLD" for the thread.