When is good time for buying bitcoins, that is individual, first someone need to have reason for buying something.
Here we come to holding, if the reason of buying is profit then best way is long term holding, for that price is still great, its under 800 $ and it will go on more then 1300 in next couple years, that means buying now is 450 $ + profit per one bitcoin in couple years. That sounds great doesn't it.
no one can exactly tell the right time for buying bitcoin that is what we only evaluate from different source, otherwise no one know that what is going to happen to bitcoin market in next few hours, so i will like to say that if your mind allow you to purchase bitcoin then you should take the risk as there is no other option without taking risk, and only then you can make money.