Mark Gregory Foster writes (concerning 1 Corinthians 16:2):

 > The idea was introduced to me once that the reason Paul wanted
 > the Corinthians to lay aside money for the collection on the
 > first day of the week was that this was when they received their
 > weekly wages.

But the ancient Romans did not observe a seven-day week.  Unless a
man was working for a Jewish employer, he is unlikely to have been
paid on the first day of a seven-day week. Nor would a Jewish
employer have kept his wages over the week-end (see Lev 19:13; Dt
24:15).