I have a view with nodes of the type 'Note' (custom CT). I have A view with comments that are associated with those nodes. How can I combine these views into one view so that I can filter them individually on the date ?
Add 'Comment' as a node type to display in the view but keep your 'Note' content type filter. You should get both the nodes and the comments associated with any of those nodes, which you can then add an exposed filter to for date.
There is no combine views together you will need to add more content fields in the view showing the Note type nodes. It sounds like you just want to add more comment fields in your view such as the comment body, title and author.
http://sethsandler.com/code/drupal-6-creating-activity-stream-views-custom-sql-query-merging-multiple-views-part-1/ describes a (code-heavy) way of accomplishing this.