I seriously doubt that he would wait for over four billion years of evolution just so that we, the human animal... could finally evolve enough gray matter to worship it.
But, if it were less time; less than 13.6 billion years, then God would be too easily revealed. As for the time necessary, you need to consider Sextus Empiricus ,"... the mills of God grind slowly but exceedingly fine ..."
Consider that after those 13.6 billion years that we are not done yet. What will we know, where will we be, or what will we be in another 4.6 billion years?