Raj,
Can you post the details like when did you send the RFE. Also, you can track your response package if it is Fedex to USCIS. That way you will know that the packet has reached the USCIS. In my last RFE, it took 24 hours - 36 hours to register into their database after the package was delivered to USCIS.
But few people here have different experience.......after all it is NSC we are dealing with....nothing is predictable......reasonable.
Mugdha.