"If you're going to invest in Bitcoin, the short time horizon is four years, the medium time horizon is ten years, and the right time horizon is forever."
Otherwise, if luck is good, everyday is the best time.
Sorry but I disagree with you, most especially with the last part of your post which states that the right time horizon to invest or remain invested in bitcoin is forever, this is completely wrong if we are to look at this critically.
It is already a well known fact that what ever has a beginning surely will have an end, if you invested in bitcoin one day, a day is also coming when you will sell that bitcoin to claim the profit it has already yielded, if you don't, your children will when you are gone (as long as they have the access to the wallet where the bitcoin is held).
If you decide to sell, and then buy in again later, that is a totally different thing altogether, but what matters here is that you have sold that bitcoins you initially bought, deciding to re-invest means you are starting afresh since you will be buying at the market price of bitcoin at that particular time.. No one will hold bitcoin forever except..
1. He or she loses access to his or her wallet seed phrase of private key, as well as also lost access to the wallet.
2. He or she is dead.
3. He or she completely forget he or she had bitcoin stored somewhere/foolish.