Jitter can also be exhibited in any lan enviroment both wireless and wired. Essentially it is measured according to a "buffer/grace" period. Anything that exceeds this buffer period is considered as being jitter. (I.e a packet that arrives out of the expected time slot)
As for the 5ms increment in latency with queues activated, hmm; not normal in my books. What ros version are you using and what are ram, cpu specs for your router. and if normal pc it might just be the lan card.