I had a heck of a time getting the AT&T Software Update OTA going on my wife’s Samsung Galaxy S5 (SAMSUNG-SM-G900A). Apparently, on AT&T images, they put a check in place on the software update to limit/inhibit multiple checks based on a timeframe. The phone did not have enough storage space on the device memory to handle the download on the first check, so we moved apps and data around to clear 3gb or so for the 2gb or so download of Android 6 and then wanted to start the update. But, you cannot just go in and run the software update again and trigger the update. There is no way to restart the updater application either to get it to recognize we had space this time. Frustrating.
Anyway, thankfully, I found this in the AT&T forums that suggests messing with the device date to get around this. I guess AT&T uses local device time to limit the request again to initiate the software update. If you take your phone off automatic date and time settings and kick the device ahead a day, the software update application resident on the phone will validate that the update can now happen. We moved the device date from Saturday to Sunday and we got the download going.
Crazy they inhibit updates in this manner, but fooling the date and time seems to do the trick.