For some reason a number field is not showing up in the Interface's filter options.
This happens specifically if you choose a layout with a specific widget (I'm using timeline in this case).
If you choose a blank layout though, the number field IS available in the filter!

What's with the inconsistency? Why would a different layout have different functionality for the same feature?

I guess the alternative would be to just use a timeline in a blank page, but I don't want to that. I prefer the feel and options when you pick the timeline layout directly.