I think you may be misunderstanding how to approach QV (or I am misunderstanding the question). You are using two disconnected island tables in your model, an advanced and usually unnecessary technique.
What are you trying to show? If you are trying to show staff count per hour then:
Are you trying to put on the chart both: scheduled headcount and actual headcount?
I think you can link those tables with a composite key like : WEEKDAY-HOUR, and later add both:
count(ID) and sum(Sch24Staff) as measures - this is solution for browsing single day at time.
You can also map Sch24Staff to the other table in the load script. I think it will be most efficient. Also for performance.