I think you should invest now, this is best time because after the fork btc might move to $7000 and by December ending $8000 is very likely
I think the best time to invest in bitcoin was that when it dropped to 3000$, i think that was the reasonable time to trade bitcoin, even now it is good option to invest in bitcoin but for long term investment, because we can expect that in future the price of bitcoin will continue increasing for along time and hopefully will easily cross 8000$ at the end of 2017, therefore still it is good to invest money in bitcoin.