Best time to buy was 8 years ago 
Next best time is now, dollar costing average is the safest way, but definitely don't just wait for the "perfect" time, because that will never come
So we need a time machine to go to the period of buying the bitcoin at the best price but unfortunately it is impossible so what can we do is buy now and hope that in future the price will increase more.But as you said there is no perfect time,so make the conditions perfect by holding the coins in long term. Next best time is now, dollar costing average is the safest way, but definitely don't just wait for the "perfect" time, because that will never come