10 to 11 minutes a day is indeed out of the normal range, it’s likely a problem with the RTC or crystal. First, can you see if the RTC on your board is DS1337 (2×10 pins, relatively big), or is it DS1307 (2×4 pins, small)? We’ve received two reports of clock issues related to DS1337, and I suspect it’s that particular batch of chips that had problems. If you have DS1337, it’s likely to be affected too. If it’s DS1307, we haven’t received reports of clock issues, but it still might be the crystal that has a problem.
The NTP sync interval can be changed in software. Right now it’s set to sync every 24 hours, but can be changed to every hour or something. This does require re-compiling the firmware and flash the controller.