PowerBI: Use filter but avoid propoagation effect - filter

Question

I'm trying to calculate how much an employee is spending time on actual projects:
'billability' = [total hours worked on projects] / [total hours that the employee was available]
I'm given a schema like:
Tornado = (employee_id, date, project_id, hours, ..)
'public employee_schedule' = (employee_id, date, hours, ..)
'Tornado' is the table that records hours spent. 'public employee_schedule' is the table that records available hours per day per employee.
So to calculate billability, I have a measure in Tornado table:
billability= Sum(Tornado.hours)/Sum('public employee_schedule'.hours)
In powerBi desktop, I have a page where I do a range of analysis on Tornado, and it includes a date filter (Timeline control) that is tied to Tornado.date
The problem: after a date range is selected, rows on Tornado are filtered and if there is no work done by the employee in those dates, nothing is selected (0 hours worked), but the filter also propagates to 'public employee_schedule' and I get also 0 for hours available.
I should be using ALL with FILTER in the denominator, but how to access the dates chosen in Timeline control?
See screenshot below for data model.

Answer 1

I created a new AllDates(id, date) table with 1:* relationship with Tornado and 'public employee_schedule' on date column.
In my page, I use AllDates.date for filtering, which propagates to both Tornado and public 'public employee_schedule'.
Finally I use Format > Edit Interactions to avoid any other unwanted filters/slicers affecting my measure (that is shown in a KPI card).
Another solution could be something along this line (WorkDone is Tornado and HoursAvailable is 'public employee_schedule') :
billability =
VAR MinDate =
CALCULATE ( MIN ( WorkDone[date] ), ALLSELECTED ( WorkDone ) )
VAR MaxDate =
CALCULATE ( MAX ( WorkDone[date] ), ALLSELECTED ( WorkDone ) )
RETURN
(
SUM ( WorkDone[hours] )
/ CALCULATE (
SUM ( HoursAvailable[available_hours] ),
FILTER (
ALL ( HoursAvailable ),
HoursAvailable[date] >= MinDate
&& HoursAvailable[date] <= MaxDate
)
)
)