Hi Steve (@SteveB)
What you need to do is pay me a million dollars!! ..... I'm kidding
Create a timeline for your Slider (make it the same length as your timeline you want to control),
Animate the ellipse on the slider left to right.
Then with the ellipse on your slider selected make this draggable by choosing Actions->On Drag->Control Timeline and restrict it to horizontal and uncheck continue after drag.
In this function you want to write something like the following (note this is pseudo code, replace the values with your own)
var time = hypeDocument.currentTimeInTimelineNamed('slider-timeline')
hypeDocument.goToTimeInTimelineNamed(time, 'timeline to control');
If you want to PM me you can. I'll send you a message.