I work as an Project Management Officer at a company that uses both Projects and Sprints. 

I've recently been focusing on my report utilization in Projects. With my Managing Partner i've been wondering if it is possible to assign users to a certain amount of time per sprint. When dealing with task i realise you are able to start a task and set a duration and estimation points. But while forecasting I can't see anything pre-hand. 

What I would like is to pre define lets say 20 hours for a specific User. That way i know that this user has 20 hours of work on this sprint. If i have to make a planning i atleast know that he isnt available for that amount of time and consider if i want to make a planning with someone else or if he or her has time.