in this day the price is so high then it is not the time to buy bitcoin wait for the price to go down like 200$ and then buy 1 btc and wait for the price to go up 
like 400$ then you wil win the double but if you buy it now and the price go down you will lose money
What if the price of bitcoin will not go down at $200 and continue increase do still wait for $200? like 400$ then you wil win the double but if you buy it now and the price go down you will lose money As I Said to my other comment if you want to invest in long term the right time is NOW. I repeat again what ever the price if you are looking term investment BUY bitcoin now and hold it.
but you don't know the future what it hide maybe today you will buy and the next day the price go to 500$ or you can buy and the bitcoin price go down to 250$ and stay like that for one year so it will be the best investment if you buy with the low price