It is hard to tell if this is the right time to buy ,
We don't know if this is the bottom of it or it would continue to sink,
But if it wouldn't go down any further then it is really time to buy back now.
We can never tell which is the best time but you can always take the risk. Also, you can sell it at a higher price anyway. Just don't sell it below your buying price. Remember the simple rule of trading-- buy low, sell high.