How to get the internal queueing time of requests sent to grpc?

Question

I want to get the time spent by a request waiting in the internal queue that GRPC maintains before it's picked up by a worker thread for execution on the RPC code. I took a look at the interceptor offered by grpc (say to add a timestamp when the request is received by the server) but after looking at the server implementation of GRPC it seems like the interceptor pipeline is executed after the request is polled from the completion queue.

Any suggestion to get the queueing time for each request before it's executed is appreciated. Or an explanation, if my understanding above is wrong, is too.