I feel one way to do that is to listen in promiscuous mode to check whether the same RREP is propagating in the neighborhood. If so, it is better to drop the RREP from a node. As for the time to do this in the promiscuous mode, that will depend on the traffic in the network. It is better to send a RREP early if traffic is low, and delay if traffic is high. 

Dear Ajoy 

  Dr Amitava asnwer it theoratically good one , Howwever i think you are asking technically how to wait. So it depends which simulator you are implementing your idea normally in simulators  like GloMoSim, OMNET there are options to send the packet with delay . Using send packet with delay option you can control sending the data packet with your desired delay.

   You may have a look at my work papers  on AODV MANET implmentation using GloMoSim. Full text available on RG profile 

1- Protection of AODV MANETs from a range of attacks using an intrusion detection and prevention system

2- An Intrusion Detection & Adaptive Response Mechanism for MANETs

3-  A generalized intrusion detection & prevention mechanism for securing MANETs

Regards 

Dr Adnan Nadeem 

http://adnan-nadeem.com/

https://www.ietf.org/proceedings/50/I-D/manet-aodv-08.txt

Thanks for answers.

Dear Sir

 I am using ns2 simulator.