Tima Data upload from External Time Mangement System

Dear Experts,

What are the prerequisites if Time Data upload from External Time Management System( data with validation).

( TMSTA - 8 schema TM00 and TM04) work schedule , absences ( lop included),comp off.

How to calculate Overtime ( IT 2010) and leave encashment.

What is the difference in configuration between negative time management and Time Capturing from External Time management system.

Pls guide me on this.

Thanks in Advance