To change the time on most NEC phone systems including the Aspire, XN 120, SV 8100, SL1100 just follow these instruction.

From any NEC display telephone leave the handset down, press the speaker button, dial 828 and enter the time in a 24 hour format ie 0930 for 9.30 am. you will hear a confirmation beep to show the new time has been set.