Though the Sabbath was originally on Saturday, I don't believe this is relevant to prophecy.
Scripture informs us exactly on this:
Colossians 2:16 Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:
or of the sabbath days << Though the Sunday worship was first done by Catholicism, and adopted by protestants. God isn't judging every Christian in the world because they worship Him on a Sunday.
Let no man therefore judge you in meat, or in drink << Nor will He judge them if they eat shellfish, pork, or drink some alcohol.
or in respect of an holyday << This is the same for Christmas. Christmas is being attacked by a select group of Christians because it originally came from the Catholics/Paganism. But God in no way is judging born again Christians who celebrate & use Christmas as a remembrance to the Nativity Story & Jesus Christ's birth. Remember holyday = holiday.
God is full of Grace & Mercy. And we are no longer under the bondage of the law. Christians worship God in Spirit. You will find a lot Christians who have there own ideas on the best way to worship God, or traditions & rituals which are not fully Biblical. But God's know each mans heart, and knows if they are worshipping Him even if it is on the "wrong" day, or a holyday (holiday) like Christmas. I believe there are even Catholics, who are full of rituals and works and traditions which are not truly Biblical, but who truly believe & seek & have faith in God & His Son Jesus Christ, and will be saved.
This is why God saves us by Faith & not works. Nearly every protestant denomination has slightly different rituals/works/traditions, doesn't mean the born again believers in those churches won't be saved.