Backup time of the devices running on ipclk

Dear LTE Experts.

What is backup time of the devices running on ipclk in case it goes down or having some malfunctions in LTE?

GPS or internal clock.
Most devices use external sources to adjust own clock oscillator and fix time drift.

This was the reply from IP team:
IP clock, unicast frequency synchronous scheme.

I need to know one more thing which kpi affect when clock lost.