Pick the lowest dip I can find say, this week, and invest all my principle. Or, dollar cost average anyway....if so, over what time horizon? Surely not over the next year. Maybe a week? A month?
If it's just for a week/month, so it's better to avoid DCA and try to get the support and resistance zone for bitcoin as well to take entry on it. But DCA will be the option if anyone's willing to hodl BTC for longer period of time because those are now on profits who started doing DCA back in 2017-18 bull run. So, it's never late for anyone to buy bitcoin or DCA on it for longer period of time, IMO.