Thanks Russ for the information and quick response - much appreciated.
FYI, our purpose for the time-slider in 3D is for transportation, construction planning and coordination, and long-range development planning/master-planning. Considering the time-slider is available in the desktop applications and AGOL 2D, along with the visual factor and importance of temporal data, I'm surprised to learn this feature somehow hasn't yet been implemented in web scenes. At this point the only online solution is an exported AVI to inform the public.
Thanks again.