There are different ways to deal with this.
A Payroll area can be created from 21st current month to 20th of next month. This would cover your attendance and payroll needs.
However, if the company needs to consider a calendar month as a pay period, then the attendance from 21st to end of month needs to be considered as per the WSR (as in the case of -ve time management).
If necessary, a WSR can have a PWS with all days off for +ve time mgt, so that time entries will determine the actual attendance for each employee.
This also depends on the type of Time Management that the company wants to use:
a)Positive Time management: Entering all attendance types - normal attendance, over time, etc, every day. In this case a default WSR is used for the employee. In this case, TM00 is the time eval schema normally used.
In this case a time entry system (e.g., Kronos) is used for clock in / out. A custom program may be needed to export / import data between SAP HCM and the time entry system. The time entry system would need employee / org data for validating entries and to export data to SAP HCM. A custom program would import data into SAP infotypes. Here usually IT 2011 will be used to record clock times.
b)Negative Time Management: Use a WSR depending on the employee's and the company's agreement. Enter only exceptions: like substitutions, OT, etc. In this case, TM04 is the time schema normally used.
In any case,
- Absences need to be entered.
- The time schema would be customized, depending on the needs.
For +ve & -ve time mgt, there are several links(see below) that you can search with Google or in SAP Help Portal.
Positive & Negative Time Management Concept | SCN
Q&A in Time Management - ERP Human Capital Management - SCN Wiki
What is Positive & Negative Time Recording
SAP HR Q & A: Time Management
http://www.soniconsulting.com/2010/what-is-positive-and-negative-time-recording/
Pros and cons of positive and negative time
Chapter 5: Time Management Configuration – Negative Time - SAP HCM - A Complete Tutorial