I don't think there will be a time that it is too late to buy bitcoin except if there is a currency that you trust a lot that will replace the bitcoin, then you should invest on that.
I don't think it's already late to buy bitcoin since it has just jump off to its highest price this year. The more savings of bitcoin you have the more profit you will have in the future. If you only have enough capital to buy it today then go buy more of it because based on the charts it will surely increase more in the coming days. Another thing is that, bitcoin might be legally accepted worldwide so many people will buy it,too.