It is best to buy bitcoin when the price is low, but the bitcoin price goes up everyday, so i suggest to buy now because its i believe it will never goes back to its previous price.
The problem anyway is still subjected to the fact that we do not know the low point yet as bitcoin has a way of ultimately surprising everyone. Like you said, buying now is still pretty perfect, whether it goes back to the previous price or not. I missed buying at $5700 because I was hoping for dip and then I missed buying at $6000 again cause I was still waiting and here I am now still waiting 
and that is what happens when you miss the right moment and end up buying higher eventually.