Time Management

Hi SAP Guru's

I have a basic doubt in work schedule. I have received a request from a client to create a workschedule i have created it .

Planned hours will be : 9:20 to 15:40

Unpaid break : 12.30 to 13.10, unpaid given as 0,67

when i give planned working hours as 5,40

in planned working time comes as 09:20 to 15:24,

My question is here end time should come as 15:40,

Depend upon planned working hours , planned working time gets adjusted automatically, why is it so. it shows wrong numbers ??

But client requesting everything in a correct way. Why its happening like that.

what actually happens in reality, can anyone explain please?//??

Thanks

Sriram