I have the same issue with a UC360 unit. All settings are what they should be for sntp to work, it just won't get the date and time. I have run ping tests and tested ntp to the time server with other devices. Everything else gets the correct time and date. I am banging my head over this. I know this is not rocket science so what the heck am I doing wrong?!
Time zone is set, format is set, use ntp when available is checked, device is registered to Mitel 5000 as a SIP phone and is calling in and out. Phone system and phones are on their own VLAN which is routed to the primary LAN. Time server is on primary LAN and the 5000 gets ntp from it successfully, a 5610 dect phone (SIP phone) does as well. What's going on here??