The sooner the better. The current price is hovering in the $50 per share range. If you want to buy in at a lower price, there are sites that offer fractional sales with nominal fees.
Stockpile allows you to buy and/or sell at what ever price point you would prefer for $0.99 per buy, $0.99 per sale with no monthly fees and no minimums.
There are other great options if you are willing to buy in whole shares.