The Linksys devices that I've worked with require that you datafill an NTP server within. They don't take time and date settings from a SIP provider (3CX in this case). One reason for this is that the set could be located in any time zone in the world and may or may not be using the same date changes for the daylight/summer/fall transitions. Using an NTP server setting in the set allows the phone to show the correct local time no matter what time/date information comes from the provider. There was some discussion in the feature request forum a while back about sending time information from 3CX to a set, which would be useful if all sets were on a local LAN that had no internet access.