Setting up groups for weekday and weekend altar servers is a common need when some servers attend Catholic school and others public school. The best way to accommodate this need this is through subdivisions. You'll want to subdivide the Altar Server ministry into two subdivisions, one that will contain the weekday servers and the other that will contain the weekend servers. Any server who can do both weekday and weekend will be in both subdivisions.
You can do this by opening up the Altar Server ministry.
1. Click the "New..." button under the subdivision list.
2. Enter "Weekday" as the internal name for the first subdivision and make sure the "Schedule label" is blank.
3. Then create the Weekend subdivision in the same way. The internal name should be "Weekend" and again the schedule label should be blank.
4. Then in the Service Times pane you'll setup your weekday services to require "Altar Servers - Weekly" and your weekend services to require "Altar Servers - Weekend".
Then only servers in the weekday subdivision will be scheduled for the weekly services and only servers in the weekend subdivision will be scheduled for the weekend services. The altar servers that are qualified for both subdivisions may be scheduled at either type of service.