Are you trying to have two extensions ring for incoming calls during the evening? if so, you can do this by using a Ring Group and Scheduled Services.
To do this, go to Telephony > Ring Groups and select a ring group other than Group 1 (Group 2 for example).
Add the extensions as members to that Ring Group.
Next, select the Line Settings Tab, and select the lines you want to use this ring group. Select Ring Group 2 for the Night Schedule.
To enable the use of the Night Schedule, go to Telephony > Scheduled Services and Enable the Ringing Svc for the Night Schedule. You can either set it as manual (where it can be enabled from the control set by using F871) or Auto (where it is defined by a sechedule).
If you decide to use a schedule, Select Night under Schedules at the top of the screen and then define the start and stop times each day (It should be noted that Start means the time it starts and runs till midnight and Stop means that time after midnight it would stop..... So if you want it to run from 5 PM Monday to 8 AM Tuesday, you'd define the start time on Monday as 17:00 and the stop time as 08:00 on Tuesday.)
Hope that's what you're looking for!