If you're holding bitcoin for long term you might specify for how long I should hold my Bitcoin, is it for 5 years, 10 years or so. But if you're holding Bitcoin for short term you should sell them once the price is going up, yeah buy low and sell high. I personally hold Bitcoin as a long term investment, even if the price is going up I don't sell my coins because I have specified the period for holding Bitcoin. when the time comes and the price is skyrocket I will sell those coins.
I am not so sure that it is the best idea to sell your coins after an arbitrary amount of time, unless you have been holding your coins for years and you have endured some crashes in the market it is difficult to know if you are still going to hold your coins in the case a negative event occurs.
I know I can hold my bitcoins because I endured the bear market of 2018 and I am still here but many people will not be able to do something like that even if they thought they could.