The best time to plant a tree is 20 years ago. The second best time is now.
The second best time is 19 years and 364 days ago (assuming you have a one day interval, and assuming that 20 years ago was the earliest you could plant it, otherwise your first sentence is wrong, and assuming the tree lives longer than 20 years, and assuming you want it to be the oldest possible tree it can be). The third best time is 19 years, 363 days ago.
Now is approximately the 7,305th best time.
Either way though, the 7,305th best time (now) is still better than the 7,306th best time (tomorrow).
:)