I can't find a straightforward answer in the documentation here. I've created a custom date table to make some calculations easier and have it functioning within one report and it's respective dataset. Is there a simple way to bring in just that table to other datasets? Also, is there a way to make it the default going forward? It gives you the option to not use auto date/time but I don't see anywhere where you can tell it what to use instead. Thanks!
No. When you bring in another dataset, it is the FULL data model, not just one table.
What you can do is create your default date table, as well as any other preferences (theme, font sizes, whatever) then save the file as a PBIT file, which is a template. Then once you start working, start with that file.
You can create a date table using DAX, but if you make changes, you cannot easily copy those changes to other files. By doing it in Power Query, I just go to the Advanced Editor and copy all of the M code to a different file. That is but one of the reasons to do the date table in power Query.