As you can seen today the price of bitcoin is falling just monitor the price here https://bitcoinwisdom.com/ and use some tools and make your own line and start speculation to your self..
Like other said anytime the price increase or drop you should learn timing when to buy and when to sell.. Just like today now is opportunity to buy bitcoins because the  price was drop from $2,700+ and now drop to $2,538 so if you invest now in bitcoin you can gain a profit if the price increase but if the price was drop more just buy more bitcoins because the price every year is increase so patience are needed in order to make a good profit in bitcoin that is why other people said that any time are good to buy bitcoins because price growth are normally increasing because of development and more investors are come..