Hours Saved Calculation with Date Slicer

I am working on a Dashboard which will identify how many hours were saved during a specified time period.

Using a Sharepoint List, connected to PowerBI, people can add their projects to the list, entering the number of hours the project saves us per Month and whether the time saved is a one-off or re-occurs monthly. For example:

PROD 1 = Saves 10 hours worth of work.

PROD 2 = Saves 10 hours worth of work carried out monthly.

When using a Date Slicer to look at hours saved over the last 6 months, I can only use the Start date as an Identifier. So therefore on-going projects like PROD 2's hours saved over those 6 months isn't included if the projects start date is outside the range. How do I create a Slicer so that when selecting a 6 month period/any time period, The hours saved during those months, and only those months, are included across all on-going projects and standalone ones.

Note this also works the other way around, for example, if the on-going project's start date is within range, all hours ever saved by the on-going projects, even those saved outside the date range are included in the total. :S Any help with this would be greatly appreciated, every solution I can think of brings me back to using the filter selected start/end dates but there no apparent way to reference that as a variable in a measure?

See Also: https://stackoverflow.com/questions/48462895/including-re-occurring-time-saved-in-date-slicer-output and Visual Rep of problem below: