Dear Anu,
First have to understand the timings for different work schedules for different employees in SAP.
You said 18:00 That is for Night Shift Employees Its not for General Shift Employees.
Night Shift: 18:00 till 3: 00 that is for Night Shift Employees starting at 6 in the evening and ending the shift at 3 in the midnight. Hope this will clarify.
For each shift there will be one work-schedule assigned to it. Employees coming at night There will be night shift assigned to it.
If you found there is some problem with employees leaving early and there is lost time then you need to check configuration If that is effecting for only one employee you need to check master data of an employee and for your scenario it is effecting for few employees. You said ,The problem has to come every month if that is the case. Are you sure employees leaving at 1 everymonth There might be a case employee left at 2 so we cant predict anything on this.
If you see Halfday its clearly mentioned timings and employees leaving 1 hour before the timings that has been defined at 2 in sap
If that is bothering you a lot why dont you test for 1 employee by recording clock in and clock out.
You can always do that and test if you are not sure that there is a problem with configuration
Regards,
Rajesh