Jesus said that the Sabbath was made for man and not man for the Sabbath. Do you really think it is important for everyone to keep it at the same time. For example, in some parts of the world several hours of Friday, Saturday and Sunday coinside during the same time period. If I'm communicating wilth someone in another part of the world my Saturday is his Sunday and his Sunday is my Saturday. Didn't the Lord give the Sabbath so we could have one day in seven to rest on. Some ministers who preach on Sunday actually use Saturday as their rest day since Sunday for them is a lot of work.