No one can predict when is the right time to buy bitcoins. As it is highly volatile. At the time of writing the current market price for Bitcoin is $10,751. If by the end of 2019 the price hits 20k or more. Then buying at this price could result in high profits. Of course, it depends on the number of units you purchased as well.
But if you aren't lucky enough and buy bitcoins at the current market price. And the price drops back around 3k US Dollars or less. You'll end up losing your investment. This makes Bitcoin very interesting, exciting and scary at the same time.
Tip:- Do Not invest all of your cash in buying Bitcoins. Just invest that won't hurt you if you lost.