What is the mekor for laying the Shabos table Friday morning, and what is it mesugal for?
Several rishonim mention that the table should be laid before Shabbos. See, for instance, Or Zarus (22), who cites the Gemara (Shabbos 119) concerning the angels that accompany a person back from davening, which implies that the table must be laid from before. Semag (32) also writes that one should ensure that the table is laid before Shabbos.
Friday after chatzos is a good time for preparations for Shabbos, since it is clear that the preparations are being done for Shabbos. There is nothing wrong with laying the table in the morning, but I don’t know of a source or a segulah involved.