Anything come of this? I've got the same problem. I get poor reception at my house, so I was using TMO wifi calling. It seems like sometimes I lose close to a minute an hour if not more. Sometimes I can go a day and still have the clock be in sync.
Now, I'm switching the radio (and wifi calling) off when at home since I have sip calling setup. Phone's been off the charger for 14 hours so far, but the radio's only been switched off for about 11 hours. My clock is 34 minutes slow currently. Toggle the radio back on and it'll sync right up again.
Looks like I'll have to use an ntp client.