If you could maintain the continuity of your service from switching from one central government organisation to the one, your all the due benifits will remain protected. Hence you should ensure in this point.
While considering your case, you have moved your application through the proper channel and even you have secured NOC in this regard. This reflects the compliance of standing service rule. However, we are not aware of the circumstances leading to delay in your release from the present organisation but for joining in the next organisation, there is a deadline and that needs to be followed for your own interest. Any delay in joining the other organisation due to less release from the present one would cause a severe setback since the next employer may refuse to accept of your joining due to expiry of deadline.
What is needed from your end is to seek an extension period from the next organisation so that any delay in the process of release can be adjusted.
Once you are released from the present organisation, join immediately to the other organisation so that continuity of your service is maintained. While you follow this step, your all benifits will remain in tact applicable to your leave, pension, gratuity etc.