Filtering Fact Table With a Date Range Based on Slider + Parameter

I have a single fact table of events, cities and event dates across a particular geographic area. My goal is a report that will help me identify the best 2 – 4 week period in which to maximize my attendance of events across the region. I already have the map visualization set up with a between slider for my event dates. But for ease of use I would like to set up my filtering as follows. AI has been very confident that it can be done, but inept at showing me how! I have a feeling it’s going to need a “complex selector” but I haven’t been able to successfully adapt what I’ve seen about those.

1. Step 1: Choose a single date using a slider that runs across the range of dates in my fact table. Ideally it would be a slider with a single ball to manipulate, but I know that might not exist. I would be perfectly happy to adjust the upper or lower end of a “between” style slider, as long as that single date value could be extracted and applied to my purpose. Let’s call this date “SliderDate”.
2. Step 2: Choose an integer value using a numeric range parameter slider. I already know how to set this up. Let’s call the parameter value X. (or any other way to input an easily adjustable integer value)
3. Step 3: Filter my fact table that feeds my map visualization such that the visualization only uses rows where the event date value is between SliderDate and SliderDate + X days. For clarity, my map visualization does not use the date column directly.

Here is a dropbox copy of my report in its current state as described above. Any help would be greatly appreciated. Thanks in advance!