Best time to invest or buy into BTC is the down periods when doubts are in and right now though price is higher then the summer the price action is lagging. You wont get the best price when gains are fast but because that gain is more immediate the majority seem to prefer this, ironically its more risky then just taking a long term view of the horizon for BTC and adding even in slow periods such as now.
Anyone in a muddle and free markets in price at least are almost completely designed to confuse the poor end user then just buying regularly is also more rational then attempting to guess every high and low per day per week or even per month.
It's also convenient in terms of monitoring the market if you are aiming for a long term goals, the chance of making decent profits is not by far for those investors who look on the long term investment compared to those who are trying to short the market, just what we know the market is volatile, unless you are really good in anticipating and you are okay with whatever the outcome of the risk you take, then it's always best not to wait but to push your strategy forwardly.
It would really be that up to you on what kind of strategic approach that you would be dealing into on which if you are really that wanting to see short term profits then you will be needing to face up that volatility but if you arent that confident about into the volatility of the price then it will be that up to you on holding up your position then it will be that up to you. Therefore, it will really be that situational into this aspect on how you would gonna deal up with these things accordingly. Investing decisions will really be that up to you and if you do find out that Bitcoin investment will be worth then holding up will be ideal, but since not all does have that patience then this is where they will be making up decisions on doing up another ways or methods.