Depends on you, when asking about the "good" time to buy Bitcoins or any market asset that you're eyeing, it's not actually mostly pertaining to the time but with your capacity to shed out a capital that could buy a substantial amount of asset, whatever that is, in order to follow through a venture. With that said, the biggest consideration here is not the price but whether you can see the bigger picture and wait out until the time the asset you bought rose to such a value that you can at least call your venture a success.