I was on a cruise ship and chose NOT to pay for internet. In settings it showed the ship's internet but noted it wasn't secure (I was not able to access wifi). My iPhone and ipad both kept the correct time and date--how were they staying in sync with date and time.
My iPhone had no service.
iPad mini 5 Wi-Fi
The internal digital clock is still quite accurate without regular network inputs to correct drift. There is no reason for any IC clock to drift more than a second or so per month in normal operation.
Every computing device has an internal highly accurate clock - the network input is only needed to correct that clock for drift over long periods of time, or to change it automatically when changing time zones.
Any iPad, iPhone or Mac should not show inaccurate time without network input, at least not over short periods of time (days, or a few weeks or so).
time and date
