Hi, if a particular improvement rate requires (for example) 10 hours, when exactly is that number of hours required? Is is the same amount of hours per week? Or should I assume that - due to the need to gradually ramp up - the hours will be increasingly slightly each week and peaking at this number?
The number will gradually increase as you progress through the training program. And when the hours are needed will depend on your usual riding schedule (i.e. if you tend to do big rides on saturdays, XATA will recommend longer workouts on saturdays, etc.)
So would the number increase to 10 hours total per week? Still not sure if that is the average, the first week, or the last week! 
I think the number of hours stands for the current week you are in.