DCA everyday such that he can have the opportunity to buy at DIP prices since the market also experiences short time market fluctuations some days, instead of DCAing weekly or monthly which he can miss DIP prices since before the time of their next DCA, the price must have increased and he keeps buying more at high prices.
It's better to do DCA each week or month or buy during the dips and that may be much better than DCAying everyday. Instead of DCAying everyday that person could also buy Dips each day and that's a better approach but still that's not going to be helpful in long term.