Please go to the path <drive>:\Program Files\Microsoft Team Foundation Server 11.0\Tools\Deploy\ProcessTemplateManagerFiles\1033\Scrum\Template\WorkItem Tracking\Process. Open the file CommonConfiguration.xml, and find the Weekends node, customize your weekends. By default, the settings are:
<Weekends>
<DayOfWeek>Saturday</DayOfWeek>
<DayOfWeek>Sunday</DayOfWeek>
</Weekends>
then run the following template coammand on "Developer Command Prompt for VS2012":
witadmin importcommonprocessconfig /collection:CollectionURL /p:ProjectName /f:"<drive>:\Program Files\Microsoft Team Foundation Server 11.0\Tools\Deploy\ProcessTemplateManagerFiles\1033\Scrum\Template\WorkItem Tracking\Process\CommonConfiguration.xml"