Which is what I advise: For the moment, hang onto those bitcoins and permit them to ride the wave. However, monitor the market closely and begin to take profits and turn them into cash or stablecoins as soon as you notice indications of a high. Then, when the bear market hits – and it will, folks, it always does – thats when you jump in and buy Bitcoin at a discount.
I believe you mean 'hang onto those altcoins', because it is altcoins that op is storing with the plan of converting his profits from them to BTC. This idea looks good in theory, but it does not mean it will turn out exactly like that, altcoins usually lack any utility and it is easy for most of them to lose their value very quickly.
My point in all this is that you could lose your money long before you try to convert it to BTC, and that is why i choose BTC over other coins and i do not fancy op's idea, but each to their own.