'Day' in the Bible

[thanking God] for your participation and partnership [both your comforting fellowship and gracious contributions] in [advancing] the good news [regarding salvation] from the first day [you heard it] until now.

I am convinced and confident of this very thing, that He who has begun a good work in you will [continue to] perfect and complete it until the day of Christ Jesus [the time of His return].

so that you may learn to recognize and treasure what is excellent [identifying the best, and distinguishing moral differences], and that you may be pure and blameless until the day of Christ [actually living lives that lead others away from sin];

holding out and offering to everyone the word of life, so that in the day of Christ I will have reason to rejoice greatly because I did not run [my race] in vain nor labor without result.