Credit management issue - delaying receivable amount.

HI All

Kindly go through the requirement mentioned below:

For eg. once I save billing, customer got debited with Rs.1200/- . Out of that Rs.1000 is the material price and Rs.200 is tax amount.

Here customer requirement is that Rs.200/- should not appear while Credit Check in the customer receivables immediately, instead it should add to the receivables only after 45 days. 

How can this be achieved?

Kindly advise.

Thanks in Advance.

Kunalesh.