
About 1 hour and 30 min of trying
I found this thread: https://www.reddit.com/r/finalfantasyx/s/DR9OEPwtNs and copied the stated method. I know it’s random luck too, so I probably just got lucky.
1st area to the right of save sphere (2 chests): open right first, then left
2nd area to the left of save sphere (3 chests): open left to right
3rd area northwest of 2nd area (3 chests): open right to left
4th area by Al Bhed Primer (4 chests): open bottom left first then rest clockwise
I got 9 chests open on about my 4th try, then 0 to 3 chests for a while. I noticed after maybe my 35th try, I could consistently get anywhere from 3 to 7 open. I think on my 50th try, I got all 12.