Adding dates to items

You will probably have to share more information for a proper response to be formulated.
My experience is that subforms are not linked to tables in the same way that top level items are. For instance, a subform with 2 date selector items will be stored in a single column of the database per the subform item in the top level table. The contents of that column then contain a JSON encoded version of the contents of the subform.

I'm not sure I'm fully understanding your problem.
Can you not add 2 columns of type "Joomla Fields : Calendar (Date selector)?
These items use the SQL field "datetime".
If you are wanting to have a one-to-many relationship, then you will have to create a new table with the minimum columns of item_id which references back to your initial item, and datetime. You would then have to decide which of those tables should have the foriegn key from the other table.
I don't think this is a CC limitation, I think it's a design question.