yes this is necessary to be able to use it for realtime data like a radar loop or lightning strikes layer. Otherwise it sits with the same time extent which gets stale once you are past the end of its original time extent. For example if I set it to hourly for radar for 7am-9am and once the clock hits 9am today and moves past it the Time Slider is still stuck showing the old data from the morning. It never auto-updates. Still not present on WAB 2.4. So for now the only use for a Time Slider is for static historical data, not realtime layers like meteorological data, social media posting , asset tracking, etc.
