[mr beer]

Chapter 10 Success Rolls starting p 343 talks about skill rolls. It refers to bonuses for mundane actions and as mentioned above, riding a trained horse for an hour or so should likely be a +4, equivalent to the book example of a "commute to work in a small town".

Time Spent discusses bonuses for spending extra (or less) time, not usually applicable to Riding but say you are trying to open a lock or tidy up a crime scene, you can swing things in your favour that way.

A non-mundane example of checking vs. Riding to mount a horse would be if you are being hotly pursued by armed bandits at the time. That's a +0 roll.