You can invest anytime as long as you have the funds. You'll gain profit eventually, only if you have patience. You just need to understand how the price works. For me the best time to buy is during at fall. Take advantage of it while others are still in panic and selling at a cheaper price.
But the best time we can invest is when everything is on the lower price so we can take the advantages to get many coins at a low price. And now, we see the best time to buy many coins while the price is the low price but if we realize, the very low price was happening in the last year, and perhaps, some of us could use that time to buy all profitable coins.
That is why we don't need to spend all of the balance we have because we could see a moment when the price is fallen deep like what we see now. But right now, I think we are a bit too late to buy at a very low price because many coins have already started to increase, but I guess, you still have time to select the other profitable coins because they are not already increasing.
Just be careful when you choose one or two coins, you need to watch closer and analyze deeper so you can buy at the low price so you won't have to worry if the price still getting down.