My set of Atma took me about 4 days hardcoring (~12 hour days) to collect. I'm sure most people would be able to collect a full set of Atma at a more leisurely pace in a week or two no problem if they don't procrastinate.

It's not that the drop rate is so low that Atma is unrealistic to obtain, but rather the sense of progress isn't very consistent throughout the ordeal and it can be quite boring.

I spent more time trying to get Atma in Central/Eastern Thanalan than every other zone combined and I was ready to pass out from boredom at times.