There is no best time to invest I bitcoin for a beginner and jts best to just buy your first portion of bitcoin and after you have matured as an investor then you can start practicing dip buy, most early investors are scared of the volatility of bitcoin so its best they use the DCA strategy that protects them from market volatility since they would be buying at every market price interval, so it's a beginner friendly strategy to start your bitcoin journey.
I understand the point you are trying to make here but you have not explained t properly. Of course, every time is a perfect time to buy sats, now, tomorrow or next week no matter what the price would be. This assurance coms from the fact that in the nearest future Bitcoin would worth more than we had bought it today in value. This is why it is not a criterion to regret that we bought it a this price and why didn't we had the chance to bought it then. The truth to this regret is that the knowledge we had now is different from the knowledge we had when we first knew about Bitcoin, we may not have held our Bitcoin till now maybe we would have been part of those early sellers who think those gains not knowing it was just the tip of the iceberg. Today they are the ones regretting more because they had the chance to buy very cheap but foolishly sold them off.