What phone models are showing incorrect time and how off are they. One thing you can try to do is update the phone config/restart TFTP Server and then reset the phones once.
Can you check and see if the phones are not running an old firmware. If yes, you should upgrade them to a newer version.
Also, the phones try to sync the time with the CallManager at 2 AM everyday. And ensure that Timezone configured for these phones are correct and match the settings of the phones which display the right time
All the IP Phones are having Date Time Group Configured as a Indian Standard Timing.
Is it we need to do any individual configuration for time setting on IP Phones?
The oddity is that the times differ on different phones. Our time was off by a couple of minutes on all phones so we ensure all of our call managers were pointed to our NTP server and under the service made sure it was set to automatic so if the servers reboot the service starts. CM 4.1(3) 7940 and 60's