'Day' in the Bible

because of your fellowship with the gospel, from the first day until now;

having confidence of this very thing, that he who has begun in you a good work will complete it unto Jesus Christ's day:

that ye may judge of and approve the things that are more excellent, in order that ye may be pure and without offence for Christ's day,

holding forth the word of life, so as to be a boast for me in Christ's day, that I have not run in vain nor laboured in vain.

as to circumcision, I received it the eighth day; of the race of Israel, of the tribe of Benjamin, Hebrew of Hebrews; as to the law, a Pharisee;