It depends if the investor is a newbie or an experienced trader. Anyone who knows crypto and can daytrade can make money in any type of market, but for newbies they should only join during a bull run when everything rises - but at different rates
Of course everyone here is a newbie when they entered the market, How can you be a experienced trader if you haven't done it before. You may have experienced in stocks or other markets but crypto is different so everyone is back to 0 when entering here.
The best time to enter is when we're in the bottom, but it's hard to identify it and there are times you're going to catch the falling knives. Just try a small amount in the beginning and see how it goes for you, if you like then they invest more but be wary of the risk involved.