If your Communications Manager Express (CME) clock and timezone configuration in telephony-service and voice register global are correct but SIP endpoints are a few hours behind or ahead (on a different timezone), you will need the timezone updater.
https://www.oracle.com/java/technologies/javase-tzupdater-downloads.html
1. Upload from TFTP to Flash.
2. Add the TFTP server configuration tftp-server flash:phones/tzupdater.jar alias tzupdater.jar
3. Update SIP Configuration and reset endpoints
voice register global
no create profile
create profile
reset