Verse 16 would indicate that “the Day” i.e., Christ’s Parousia indeed fits that bill…
…in the day when God will judge the secrets of men by Jesus Christ, according to my gospel.
This is not dissimilar to Paul’s words to the Athenians where he says…
Acts 17:30-31 Truly, these times of ignorance God overlooked, but now commands all men everywhere to repent, because He has appointed a day on which He will judge the world in righteousness by the Man whom He has ordained. He has given assurance of this to all by raising Him from the dead.”
Said judgment was ABOUT TO fall… that is the meaning of the word translated “will” which should be translated “about to” thus showing its approximate immediacy. The word is <μέλλει> mellei from <μέλλω> mellō = “about to”. Here are a few examples…
Mt 16:27 For the Son of Man is about to come in the glory of His Father with His angels, and then He will reward each according to his works.
Rom 2:23-24 Now it was not written for his sake alone that it was imputed to him, but also for us. It is about to be imputed to us who believe in Him who raised up Jesus our Lord from the dead.
Mt 17:12, 22 But I say to you that Elijah has come already, and they did not know him but did to him whatever they wished. Likewise the Son of Man is also about to suffer at their hands.” … Now while they were staying in Galilee, Jesus said to them, “The Son of Man is about to be betrayed into the hands of men.
Also Paidion… any thoughts as to my request back up the thread HERE?