Running

Are these things just a guide?

Yes.

Although the figures get more reasonable if you're using the Garmin regularly and Connect has a reasonable grasp of your training status. At least it does for me. Rarely says over 24 hours recovery unless I've just finished something really big for me. The only time it owuld say something like 60+ hours is if I've had a few months off or not been using my Garmin to track activities.