Hello, I have similar problem. I tried your way with NTP server, but for me it doesn't work. Audio is out of sync.
I've tried the firmware V2.800.0000005.0.R.190325 and V2.800.0000010.0.R.190807 - after few hours audio is delayed.
In firmware V2.800.0000013.0.R.191202 - after few minutes video...