I'm confused. Sorry!
I've read on the forums and wiki that one can spend favour to reduce the learning time by half. What does that actually mean? Is it the total time (which it doesn't seem to be, but I may be wrong!), or is it the remaining time (which it can't be, else one would never max out the speed, unless there is a little-known Giant named Zeno), or is it something else?
If I have a skill that starts off at 24 hours to learn, and the associated primary giant has a favour cap of 1000 (just to keep it simple, and ignoring secondaries for the same reason), in one game day I can reduce the learning time by (999*10/60/60=) 2.8 hours. The next game day, I can take off another 2.8 hours, and so on.
So, if I play diligently, after 12 hours, my skill learning time is reduced to (24-(12 hours of actual time)-(2 game days * 2.8))=9.4 hours. Except that that is reducing the total time by more than half: if I try and do that (ignoring the inevitable errors in my calculation), will I max out the learning speed? I haven't done the maths, but I don't think that that's what's happening (I've been doing donations at more than 1000 cap and not noticeably hitting the cap in two game days).
Can someone point out the error in my workings, please?