It has been available in Geany for a long time as a plugin but I remember an article by the Geany Devs explaining why they did not really like it... It had a humorist sort of title, something like " Everything you never wanted to know about saving" or something like that.
I don't think I said anything negative about the plugin autosave in that wiki article, except perhaps that it makes all the disadvantages of the saving methods (the whole point of the article) happen more often, and if backup is set will fill up the disk if the user doesn't clean up every so often, although thats less a problem with modern disk sizes than it was back in 2013 when that was written (sigh! feels olde).
The auto-save interval was set to 5 minutes, if I remember correctly. I tried to make that much shorter, but had to stop at 5 seconds...anything shorter caused instability.
That was before version 1.38, which I only found some weeks ago. In the new version, I can speed up the interval to 1 sec! That's close to instantaneous.
AFAIK nothing changed in Geany in that area, but maybe the background libraries improved.
...
I would of course have preferred LiveReload as Emil Axelsson suggested. I tried but did not succeed to get the background service running. I tend to be a little impatient, but a browser add-on should just work out of the box imo. TaB reloader is the only one recommended by Firefox, it has 71.673 users, compared to 990 for Live Reload...that's telling something too.
Or maybe change browsers ;-P 1,000,000+ users https://chrome.google.com/webstore/detail/easy-auto-refresh/aabcgdmkeabbnlee... or 400,000+ users https://chrome.google.com/webstore/detail/auto-refresh-plus-page-mo/hgeljhfe...
Cheers Lex