So I don't know if it's because Shai doesn't have anything set up for mounted combat or if it's because she rides donkeys, but it seems as if she cannot do mounted hunting with a matchlock. I know she's gonna get horse riding eventually, it looks like, and I don't know if this is a separate issue or not, but this appears to be an issue. I do this time trial quest as fast as I can on foot and it still says I'm too slow. Thought I'd try it mounted, but it doesn't work.