I have supposedly saved 25 months.
Intriguingly, the ten macros I have used most have saved me no time. These are mostly little parsing and text extraction tricks I need to support my main macros.
I use KM for a range of things, but I would guess most of the heavy lifting is done by a small group of macros that lift data from an incredibly unfriendly SaaS database and then generate batches of emails, report skeletons and updates.
I assume that KM is calculating the time save typing in this instance, although to be fair I run the macro on a fairly regular basis to refresh something and so it will often be doing a lot of work it has done just a few hours earlier 
I’ve been running for it year; 760 times and it managed to save 19 months in that time…
Anyway, that’s automation for you. I’d sooner maltreat my system than my neurones.