Luke 16 makes clear that upon death Lazarus immediately went to a heavenly place of comfort and the rich man immediately went to a hellish place of misery. (Likewise the thief would go to Paradise "today," Jesus said.) It is God who judges the conditions of their hearts and where they should go.
I agree that there is a final judgment, but Scripture shows that there is also an immediate comfort in heaven or suffering in hell at the point of death. A parallel might be a prisoner who is on death row. The sentence hasn't been carried out, yet he is still in a place of preliminary punishment. In fact, even before he is convicted of the crime, he is in prison awaiting a final judgment. Because God the righteous judge is all-knowing, He can without error assign someone to comfort and someone else to punishment even before the final judgment.