Need help in preparing Summary report through excel vba

I need a help in preparing a summary report of regular intervals through VBA. Please note the time in the first column of the source data , below date is in IST format and the output needs to be in CST. The difference is in 11:30 hrs(-), i.e., the output time should be 11:30 hours shorter. To illustrate, the data for 6/19/2012 for Agent Name & ID: Mridul Aggarwal - 4758, at 21:45 is actually 10:15 for the same date. Whereas for 6/20/2012, at 00:45, the data is actually for 6/19/2012 13:15 in output.

PFA the source data in sheet Agent Wise Raw WE ; 24th June and Individual which is the output.

I would appreciate if you can also send in the algorithm.

Thanks in advance,
Compumast