The following image illustrates the accumulated delays during the transmission of UDP packets. Starting with a 1 second sleep with theoretical no delay, but practical delay of ~200 microseconds on a un-busy box till due to timer granularity and concurrent processes (not in this scenario), till transmission delays via intermediate routers, NIC interrupt moderation and finally RX side scheduler latency.

!http://blog.jauu.net/2010/07/20/UDP-TX-and-RX-Delays/udp-rx-tx-delay-thumb.png!