Some time ago I was watching a video on youtube when someone who has been trading bitcoin for a while says the time to sell bitcoin is when altcoins start to rally. If anyone knows who this youtuber is please let me know.
Stop following the YouTubers and you will be better positioned in this market. I haven't have a good experience with the majority of the crypto YouTubers as their motive is to get the views and you can find them saying everything from bear to bull perspective and one of the two things usually gets right and they start to claim that they predicted the market. I am not saying everyone is doing this; there may be exceptions, but the majority of them have no idea of the markets.
Usually, when the bitcoin tops, the altcoins top after a few weeks but it is a time of extreme caution as if you got into new positions at those times, you might find yourself stuck if the market dumps unexpectedly.