Hi Sheetal,
Please check the link - http://scn.sap.com/thread/1775077
The link - http://www.attsuppliers.com/downloads/OCI_40_EN20030611.pdf has a copy of the documentation on OCI 4.o. Section 4.2 of the document lists the fields that are transferred from the punch-out catalog to the SRM shopping cart. One of the fields is - NEW_ITEM-LEADTIME. This lead time is used by the system to calculate the delivery time of the line item in the shopping cart.
The first link would be of help in manipulating the standard behavior of the system.
Hope this helps 
Cheers,
Yateesh