I also read that some sites may do weekdays, but never heard of anyone actually doing it.
As for Sabbath observance, only you can decide if it is "OK" for you to break the Sabbath.
I had to make a decision as to if I would work on Sundays. I decided I would not purposefully schedule to work, and told the person who does the schedule I do not want to work Sundays. I am required to work 6 weekend days in a 6 week period, so I work every Saturday. In the past year, I have only had to work 5 Sundays (the person opposite me for 3 months also wanted to attend Church, and I could not in good conscience allow them to not be able to go while I did, so we split the Sundays).
As for the CPNE, it is a one time deal (hopefully
) and I felt that it was OK.
As said, contact your EC advisor.