This made me curious, I had no idea of transmit-to-response timing, so I checked it out. On a very simple two-node network, the time from sending a Transmit Request packet (0x10) with a very small data payload, to getting the Transmit Status (0x8B) back, is typically in the 28-35mS range. The first packet after power-up can take quite a bit longer, 150-200mS, and I saw one ~600mS. I assume the XBees are setting up their address tables on the first packet so that may account for part of that.
BTW, I don't transmit then wait, or not exactly. In the loop() function, I check the XBee as often as I can (however fast the loop runs) for incoming traffic, with no delays involved. Transmissions are timed, and I usually only transmit every 10 to 60 sec. As soon as the transmit request is sent to the XBee, the main loop goes back to checking for incoming traffic, and at some point the Tx Status packet comes back.
As for where to post, I might have chosen Networking, Protocols, and Devices. But I sure wouldn't lose much sleep over it