After you die, would you be able to talk to God at judgement day and ask for forgiveness? Or do you have to confess your sins when you’re alive? Also, what if an Atheist died and then saw God at judgement day? Would it be to late for the Atheist to say "I believe in you, please forgive me?"
How many people do you think are in hell today?
“For we must all appear before the judgment seat of Christ; that every one may receive the things done in his body, according to that he hath done, whether it be good or bad. Knowing therefore the terror of the Lord, we persuade men.” (2 Corinthians 5:10-11) According to Paul we will be judged according to what we do here on earth. Thus it would be too late to ask for forgiveness, or for the atheist to ask for forgiveness. Since we are commanded to be immersed in water for the forgiveness of our sins, it would be even more difficult for the atheist in your example, or anyone who had not obeyed Christ during his life.
I have no idea how many people are in hell today. What is more important is to make sure that is not where I will be.