Hey Brad, hope this finds you well. I apologize for the delay in getting a response. Could you clarify the type of time slider you would like to see in Insights? Time enabled content will typically work in Insights cards but I have a feeling that you are speaking about a ArcGIS Pro like time slider.
Unfortunately it does not seem like we have this within the product at this time That being said, you are able to create and use a time series graph. This might prove to be a workable alternative for you. Please let me know if you have any questions.
No worries, I've moved to developing my own app/dashboard.
That is correct, time enabled maps are not supported in Insights. That being said, you are able to set up a scheduler in Insights 2020.2 running on ArcGIS Enterprise 10.8.1. More info on this can be found here: Schedule updates for shared pages