Daya,
The answer depends upon how you have configured your Availability check. OVZ9.
If you have left unselected the checkbox "Check without RLT", then the system can use Lead time to calculate availability. In general, for manufactured materials (not externally procured) the system will by default use "Total Replenishment Lead time" in the material master to generate confirmations for the situation when there are inadequate supply elements to confirm the order. If the TRLT field has not been maintained, then the system will use the sum of inhouse production time and goods receipt processing time to confirm. For more info see F1 help under "Total Replenishment Lead Time".
Best Regards,
DB49