Hi,
as standard you can exclude sla calculation only by defining customer status.
but try via assigning lunch time in factory calendar, might affect in sla.
you can also define the date rules in date profile, assign the date profile in your ztransactions, you might achieve this requirement.
refer the section,
2.6 Settings for Durations
here SLA Management - SAP IT Service Management on SAP Solution Manager - SCN Wikia
check the same here in section 4, Incident Management: SLA configuration hints for SAP Solution Manager 7.1
check and update
Thanks
Jansi