Bitcoin is the best crypto coin in the world and one of the best investment right now in the world, and buying Bitcoin and holding is very safe the reason why I said is safe is because Bitcoin is a fast growing asset and if you start accumulating and holding now in the future you will make good profit from it, if you go through the history of Bitcoin growth you will know that truly Bitcoin is a good asset to hold unlike Altcoin, it is true that Bitcoin is volatile in nature but Bitcoin volatility those not stop it from growing there was a time Bitcoin was $1k from that to $5k from that to $10 and now is very close to $100k, Bitcoin is always growing is not like Altcoin that don't grow, some Altcoin coin has been in a particular amount for years now the only time they get a rising and falling state is when they lunch them after that time it becomes stagnant.

About your question that when should one buy Bitcoin, There's no time that is given for one to start accumulating Bitcoin except you are a trader because traders they usually buy when there's a dip and then sell when Bitcoin rises in a very short period, as an investor there's no right time to start Accumulation as long as you have the financial strength to accumulate you can start, is not actually good to wait for a dip before you can start accumulating because it will delay your accumulation journey.