What we need to know about that day, is that there is only one of them. You will meet Christians who speak of several days of judgement and they believe that when we read separate passages in the Bible about the day of judgement, that they are all different days. However, the right perspective is to see all the different passages in the Bible that speak of a final judgement are all describing one judgement. There’s only one final judgement.
In terms of when that day is coming, you’ll recall the Lord Jesus saying that ‘about that day or hour no one knows, not even the angels in heaven, nor the Son, but only the Father.’ All we know is that it will come like a thief in the night, and so we need to be ready.
And then, as we think about this we might get to the point where we realise that God already knows what we have done, and so has already judged everyone, so what’s the point of having a final judgement day? But the reason for the final day of judgement is not so that God can find out what we’ve done (he already knows that) rather it’s a proclamation; it’s the day on which every creature gets to see what God has done in saving his people and in judging the wicked as described in Psalm 1. The whole point of this day then is that—unlike we have it now, where there is secret judgement taking place—there is going to be a day when it is all made public.
To which we may think, “well, if there is going to be a day when the Lord Jesus publicly judges all, how do we know that the Lord Jesus is fair? How do we know that the Lord Jesus is going to judge rightly?” Well, the Bible is very clear on the impartiality of the Lord, no one will be able to say that the Lord has treated them unfairly. As John says in Revelation 19, ‘his judgments are true and just’. And that’s good news for the church, because we are being judged on the basis of the behaviour of The Man of Psalm 1, and not on our own behaviour.