It shouldn't take all that long to set up USB. Getting the host controller running is probably a few hundred microseconds of initialization. After that, it's all about enumerating hubs and finding devices; there isn't much there that requires delays. You're probably gated by the firmware on the keyboard.
I imagine the USB stacks are full of paranoid "let things settle for 200ms" sleeps that make more crappy devices work, or that give external HDDs time to spin up. I'll bet you could remove those if all you care about is a keyboard.
I imagine the USB stacks are full of paranoid "let things settle for 200ms" sleeps that make more crappy devices work, or that give external HDDs time to spin up. I'll bet you could remove those if all you care about is a keyboard.