Samstag [bes. westd., südd.] [österr.] [schweiz.]
Sonnabend [bes. nordd. und ostmitteld.]
No. They are synonyms. I would argue that Samstag is in more common usage if you want to address an audience across all of Germany. The Tagesschau daily news program, although being produced in Hamburg uses Samstag (compare the weather forecast at the end of last Friday’s report). The regional weekly newspaper in Braunschweig (Neue Braunschweiger) consistently uses Sonnabend.
I also noted that the speaker, Jan Hofer, even though being from the North used the decidedly Southern pronunciation of Samstag and 28. ending in /k/ rather than /ç/ or /x/.
There could be a tendency of Notherners to replace Sonnabendabend with Samstagabend to avoid repeating the Abend, but I don’t have enough data to confirm that.