Doesn’t matter too much over the long term, meaning over at least 10 years. Daily is better for dealing with volatility so you’ll technically gain closer to the real return of the stock. But if you buy every month, it should average out, so sometimes you buy 3% too high and sometimes 3% too low. But there is more risk in the latter so I would say putting money in every day is better for long term investing, but again shouldn’t be a big difference between the two