Sharing what I still know from my farming, I didn't note down exact numbers but this is how it went for me:

Tuesday: Farming Occult Crescent Fates and CEs from 1pm to 1am (with some breaks and also finishing up the zone story), also did a few fates to check the drop rate which dropped 2 Living Memory Atma, and ended up with 13 Atma iirc, one extra
Wednesday: Farming Occult Crescent Fates and CEs from 2pm to 6pm, at which point I only missed one Urqopacha Atma which I farmed with zone Fates until 7pm (maybe 20 Fates, lots of waiting for them to spawn)

I was not yet knowledge level 20 when I finished (I would have been if I didn't go for zone fate farming for the last Atma) and completed less than 50 Fates and CEs both since I got the achievements for both after my first relic. I had around 5 extra Atma iirc. I did approximately 40 of CEs and Fates each, so 80 in total for ~20 atma for 25% drop chance. At worst, my OC drop rate would be 98 (49/49 CEs/Fates) for 17 Atma, which would be a 17.34% drop rate, but I did get a few extra Atma from OC, so this is just a lowest estimate. As for shared Fates I did maybe 30 Fates for 3 Atma, so a 10% drop chance there. 40 Fates would make for a 7.5% drop chance, but I'm not sure how many I actually did, so those are just rough guesses. Overall I spent maybe 1 1/2 hours on Fates.

Compared to what I've heard and seen from other players and friends, this is an extremely high drop chance. I finished the grind ~33 hours after server maintenance was over, but I spent roughly 16~17 hours on it.