You've been told DCAing is the way

And yes, making it a habit to change extra fiat money into hard money is good hygiene.

But should you do it daily? weekly? monthly? quarterly? even ANNUALY?

I did the calculation for you

Assumptions:

Principle 5 MJPY

Stack Start Date: August 1, 2017

Stack End Date: August 10, 2023

Stack Interval / Stacked BTC / Current Value in JPY

Daily 3.18 BTC 13,541,038

Weekly 4.23 BTC 17,990,624

Monthly 4.33 BTC 18,424,874

Quarterly 4.60 BTC 19,578,888

Annually 5.63 BTC 23,944,591

So based on the above assumptions, longer intervals led to better results

Which was counter to my expectations

The backtesting can be performed by changing the above parameters, even on assets other than bitcoin so let me know if you want to take a spin