Unfortunately we just don't know. Many people have tried to figure out when he will come back, or what conditions are required for him to return, but quite frankly they aren't specified and we are to be ready for his return at any moment.
Matt 24:35-37 (NIV)
35 Heaven and earth will pass away, but my words will never pass away.
36 “But about that day or hour no one knows, not even the angels in heaven, nor the Son,[a] but only the Father. 37 As it was in the days of Noah, so it will be at the coming of the Son of Man.
Honestly there is no telling when he will come back, but I can guarantee that no one will expect it when it comes:
Matt 24:41-44 (NIV)
42 “Therefore keep watch, because you do not know on what day your Lord will come. 43 But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into. 44 So you also must be ready, because the Son of Man will come at an hour when you do not expect him.
All this to say we don't know when or under what conditions he is coming back. In fact its pretty clear that we cannot know and that we will not be expecting him.
As to the second half of your question, God knows what he is doing. Even though more people are going to hell every minute that the earth continues to exist, more people are also coming to Christ and more people are being born who will become followers of Christ. You are looking at the pessimistic side, but look at the good side God is saving more people every day the world continues to exist.