Curiously, I set the Window size all the way down to 8 = most wideband (was 1024). Still updated in 5-second chunks. Just for fun I tried 32768 = most narrowband. Still updated in 5-second chunks although display was much choppier.
Sorry my mistake*, I was thinking of the time taken to render the spectrogram of audio already in Audacity,
rather than rendering in real-time as it is recorded.
[ * In my defence, I was using a computer which did not have Audacity when I wrote that post, so could not check ].
Audacity’s competitor OCENaudio displays the spectrogram of recorded audio in less than a second
Like Audacity, OCENaudio is available, for free, for PC, Mac & Linux.
It’s not as powerful an editor as Audacity, but you could transfer recordings to Audacity for editing.