Some day in the future, you will realize that the best time to invest was not today, but some other day in the future, when prices were low. But with the information that you have today, the best time to invest is still today, because you do not know when prices will be low, and you do know that the longer you hold your investment, the more time it has to grow.
It depends how much you need or value the money you have now versus what it could be in the future
Of course when applies to Bitcoin earlier is better in general although there were still times where it would take a long time to get your money back buying at peak prices in 2013 to 2017 but yes in general investments do need time to grow and that builds their value.
There's no better word than "today", I don't know how many lowest point of
BTC of this year especially after the emergence of hardfork, but $900- $1000 for one
BTC is good enough to invest. Bitcoin prices determined by market and it starts from you/each person. If you choose to wait, market price movements will also be waiting.