Surely a properly designed debounce circuit would add zero latency. If you only have to worry about false deactivation and there's no line noise, and your keys

Surely a properly designed debounce circuit would add zero latency. If you only have to worry about false deactivation and there's no line noise, and your keys always stay down long enough to be caught by your scan interval (or they trigger an interrupt), then probably yes. If you have to worry about false activation, then probably no.