Problem:
The user would like to filter two views with the same date filter.
Solution:
Each view needs to have its own filter. Custom code is required to hide, and synchronize the filter, of the second view from the first view.
Because the views are using AJAX the custom code needs to be run when the views update. Check an example here https://toolset.com/forums/topic/1-date-filter-for-different-views/#post-2239831
