I might give this another stab but I don't intend to spend a lot of time trying to make it work.
I'm not flashing any images that aren't release versions. I'm still on 4.0, and now using a hybrid of transponder time with Bars & Tone as a startup service/parking channel, and NTP time otherwise, and it works perfect for me.
The reason time goes wonky on some peoples TNAP when set to NTP time AND using standby mode, is because for some reason, TNAP WANTS to sync to transponder time over NTP time. So, when on a channel/transponder with the wrong time, it'll wander off all by itself at intervals. Having NTP time set to 5 minutes, allows it to self-correct.
Once 4.1 gets released, I'm going to flash it to an empty slot, and set it all up from SCRATCH. So, it can't pick up any "corruption-cooties" from a previous backup.
I highly recommend anybody else to do theirs from scratch also, IF they want to upgrade. With 4 slots, there's no reason to not do so, beyond it taking time to do a complete setup again.