I’m just setting up a training plan for a gravel event at the beginning of May.
When putting the maximum number of weekly hours in do I use Xert hours ie including all the coffee stops I do when outside riding or do I use the actual riding hours I can do.
Go with actual hours.
It is really a XSS constraint, assuming you can generate 60 low XSS per hour. You can overcommit your availability a bit if you intend to produce a bit more per hour. Or less if you intend to hang out at the coffee shop 
You can set it for the riding time you have available. If you need do to a bit more in order to meet your event/goal, Xert will let you know ahead of time.
I think you need to consider both.
The model requires the number of hours you actually ride.
Nonetheless, the hours you ride is a subset of the number of hours you actually have available because you need to change clothes, shower, and so on. I have seen people confuse the two and as a result have problems.
I can appreciate that Mike.
To clarify, the ForecastAI doesn’t prescribe training by duration, it prescribes training by XSS, which is then calculated into estimated duration, assuming that most rides accumulate about ~60 low XSS/hr.
As a side note, workouts with relatively low focus durations (e.g. 2-5 min power) are a bit harder to accurately estimate duration for, since workouts/activities with a pure focus will require periods of very light recovery (closer to ~40 XSS/hr) between the pure focus efforts (often well over 100 XSS/hr) in order to facilitate enough recovery to keep the difficulty low while still achieving a PURE rating.