Time Periods 
A set amount of time that you use to perform tasks such as viewing reports and retrieving data.
You define time intervals for production shifts and reporting periods.
You reference time periods in the following places:
Web pages
Applets
Queries
Hyperlinks
To add, edit, or delete time periods, on the SAP MII administration menu choose
You cannot edit or delete the following time periods, which are defined by the system:
CurrentMonth
CurrentShift
CurrentYear
PreviousMonth
PreviousShift
PreviousYear
The CurrentShift and PreviousShifttime periods are used with schedules.