5 hours isn't too bad. My first took about 8 hours and 1 took around double that. But I also received my 2nd in 2 FATEs (after getting my first), my 4th in 3 FATEs (after having a break for a few days after getting my 3rd) and my 5th last night in the first FATE I took part in while waiting for CT.
I haven't bothered much with Atma, I now have 5 in around the 4 weeks since getting Stardust Rod Zenith. I just do FATEs if I'm in the area and waiting for DF, or if I have nothing else to do.
Don't expect the drop rate to be increased any time soon. If they increased the drop rate now, everyone who grinded ages for Atma would've wasted their time. Maybe in a few more patches, but for now we're stuck with it as it is.

Good luck getting your Atma.