When trying edit date (or any property, really) of an existing series via "Edit series", no save or update button is showing in order to update the value you've changed.
After updating the value (for example, changing the date from 24th of every month to 30th) there is no way to save the new value. Only option is to close the window, which Prompts "Are you sure you want to discard all changes?"
Seems the behavior is the same for any type of series.