OUTDATED WITH 2.4.4
For now, it is impossible to use strtotime()-compatible strings in Dynamic Visibility conditions.
Yet, if one needs to show certain widget(s) depending on the meta fields values of date type,
there is a solution.
For example, you have a Date type meta field "start-date",
and you want to hide certain widget(s) dynamically -
show widgets if "start-date" is in the past.
1) Create a Listing of post type you want to hide widgets dynamically on,
put needed widgets into it;
2) Place Listing Grid with that Listing on a page,
and set queries:
The first query item is needed as we only need one Listing Item, and the information in it should be pulled from the current post.
The second query item will sort out Listing Items, that have "start-date" in the future.
As the first Item has excluded all posts but current,
the query will have the result only if "start-date" is in the past.
Also, set Widget Visibility to Hide widget if Query is empty:
(so that you will not have No data found on the page)
If you are using this method in the Single template,
In Elementor the query might be empty;
however, if everything is done properly, on the live page everything will work as intended.