Dickens manipulates time in several ways in A Christmas Carol. When the Ghost of Christmas Past visits Ebenezer, rather than talk about past events in memory only, the ghost is able to visit the events in real-time, as if they were happening at the present moment.
When the Ghost of Christmas Present visits, there are still a few flashbacks, this time to the not-so-distant past. Ebenezer is able to see things (again in real time) that happened earlier that evening.
Finally, when the Ghost of Christmas Yet to Come visits, Scrooge and the ghost flash-forward (as opposed to flashing back) and visit scenes that are yet to come with the same real-time vividness. Dickens manipulates time in this way so that Scrooge sees these scenes as they happened, as opposed to seeing them through the filter of his own memory. He is a third person, as opposed to a 1st person, in witnessing the events.