I think it was 11 pm because he tells Scrooge that he will be visited by 3 ghosts starting at midnight
Marley told Scrooge that three spirits would visit him: the Ghost of Christmas Past, the Ghost of Christmas Present, and the Ghost of Christmas Yet to Come. These spirits would help Scrooge see the error of his ways and lead him to redemption.
That the first ghost (Christmas Past) would appear at mid night - as to what the purpose was marley only states they (The Ghost ) were there to help Scrooge
The first of the three would visit at midnight
As the clock strikes one
Three Spirits
at 1 am
Marley tells Scrooge to expect three more spirits to visit him that night.
Marley appeared to Scrooge and warned him about changing his behavior. Marley also told Scrooge he would be visited by three ghosts.
Marley told of three ghosts
When Marley's ghost visited Scrooge he warned him about the ghosts and his behaviour.
Marley's visit to Scrooge shows that he is regretful and burdened by his past actions. He warns Scrooge to change his ways to avoid the same fate of being tormented by regret and chains in the afterlife. This visit demonstrates that Marley still cares for Scrooge's well-being, despite their past business partnership.
The first ghost to visit Scrooge in "A Christmas Carol" is the Ghost of Christmas Past. This ghost shows Scrooge scenes from his childhood and past in order to help him reflect on his life choices.
Three ghosts
Three were foretold
Jacob Marley was Ebenezer Scrooge's business partner in Charles Dickens' "A Christmas Carol." He was the very first ghostly visitor to Scrooge on Christmas Eve to tell Scrooge that he would be visited by three other spirits that night. The opening sentences of the book are "Marley was dead: to begin with. There is no doubt whatever about that."
Jacob Marley tells Scrooge that three ghosts will visit him to warn him of the consequences of his actions and show him the errors of his ways. The three spirits represent the past, present, and future, aiming to prompt Scrooge to reflect on his life and make a change before it's too late.
Marley's ghost visits Scrooge to warn him about the consequences of his selfishness and greed. Marley states that three spirits will visit Scrooge over the next three nights to show him the error of his ways and offer him a chance at redemption. This encounter with Marley serves as the catalyst for Scrooge's transformation throughout the story.
This was Marley telling Scrooge that he (Marley) was allowed to come back to Scrooge to tell Scrooge of his inpending eternal life of torment should he not make changes to the way he lives his life now and sees mankind as his business not just the money he can get from them