An issue has been found with the "Sending schedule" setting not saving the first time with the following scenarios.
Add a cycle time, but no start date and end date.
Appeared to save but gave no error but then cycle time was blank.
Add a cycle time, added a start date but NO end date and added a recipient filter
Got a 500 error.
Also, there is another confusing message in the listing view of newsletters the sent column says "Sent on, date/time" when a draft.