20 minutes is not super fast
I'll do it that way though makes more sense at least after I have collected all the armor sets from my amiibos
The process is faster. The amiibo is basically a 10-15 sided die and you are rolling hoping to get one side. Your way had you going into the system settings every time you rolled. The other way is just pausing and reloading your save. So yes 20 minutes isn't super fast but you're rolling that die way more times in that 20 minutes reloading saves than you are changing the system's date. Which means that you are gonna roll the side you want that much faster.
And, if you wanna talk about fast, it took me
over an hour to get the Sword of Six Sages from Ganondorf's amiibo, and then from muscle memory of reloading for an hour
I reloaded and erased it instead of saving. It took me another 30 minutes to get it again.
So. Yeah. The roll rate on the really special items is fucking crazy low. Might as well maximize how many times you roll for the duration you're trying, right?