From the perspective of technical analysis the best time to "jump in" is when the price drops by 60%. Beside that you should also consider that this market is really volatile and you should never put all or your speculative money in at once.
The bitcoin price is already trading in a very very low price, it was trading in such a low price for a long time and therefore we are not expecting any further decrease in bitcoin price, but will hopefully now recover and very soon we will see the bitcoin price trading in a very very high price, hopefully bitcoin will very soon reach to 30000$.