The timezone thing is just a placebo, I tried 2 zones at their specific JP times 2 days in a row with no drop. Luck based RNG is just that. I went about 20+ hours of farming, an hour or 2 a day, and only ended up with two atma. Yesterday I sat down and went on the grind hard, and was able to get the remaining 10 atma in about 12 hours total (Soloing boss only fates in a few zones was my huge time sink).

Just keep at it, and eventually you will get the atma, may RNGesus be with you.