Well, from what I see (and did myself as well), trust me, when people say "farm for hours", they do mean going from one FATE to the other non-stop. Or, well, y'know, with reasonable stops, like bathroom breaks and eating and the like. But yeah, definitely not just standing around one FATE pop spot.
As for hours, I've no idea how much I've put in - I just got my first atma weapon yesterday. The number of FATEs done is easier to track with the FATE-related battle achievements - for whoever's not aware of this.And yes, it does get literally mind-numbing. If you're braindead by the time you get your atma recolor and can't even be happy for it... I don't think anyone's gonna blame you.