There is some information I hope it can help you:
To update the phone display immediately do:
<reg-date; => and send the command result to the system ( in older versions, need to do twice).
e.g.: CHANGE-DATE:WEST,360,DST,60;
Note: CHANGE-DATE should not be used during high traffic because it forces (beside other things) immediately time-update of all phone-devices. Several individual messages per device will be generated in the BP and transferred all the way down to the devices. In large PBXs this will produce a lot of traffic and big load in the BP and in the LTUs. It will take several minutes to process all devices and may interfere with other CP-activities. (Calls may be delayed ...). If still the same, restart SLMO cards...