It only takes a few minutes to lock in,
then turn it off and you should be good for at least a day or two
(if you are trying to maintain 'informal' accuracy).
If you are after continuous millisecond accuracy then
maybe you need a different piece of hardware.
In that case even the NTP sync done through the variable latency
of a Wifi or GSM link is going to cause jitter.

GPS time is the very highest accuracy you can get in consumer goods - even NTP uses GPS as Stratum-Zero

HTH