Do you wonder about the word anytime at any time? Anytime I stop to think about a word before I write it, wondering whether it is one word or two, it seems like a good topic to write about. If it takes me any time to think about it, I assume you may be thinking about it too.
That paragraph illustrates the use of anytime and any time.
Any amount of time = any time.
Do you have any time to review this piece?
We spent hardly any time in Dallas.
He doesn't have any time for us now that he has a girlfriend.
Whenever, at any time = anytime.
Call me anytime.
Anytime this happens, let me know.
I can meet anytime on Friday.
The correct choice after the preposition at is always the two-word form. Or leave out the preposition and use the one-word form. (Leaving out the at seems to be an American habit.)
I can meet with you at any time. (Compare: I can meet with you anytime.)
Did you talk with him at any time? (Compare: Did you talk with him anytime?)
I am free at any time between 1 and 4 p.m. (Compare: I am free anytime between 1 and 4 p.m.)
In case you are spending any time wondering whether I made up these distinctions, I didn't. I checked Garner's Modern American Usage, Fowler's Modern English Usage (Revised Third Edition by R.W. Burchfield), and The Gregg Reference Manual. The other reference books on my shelf did not address the topic.
If you have any time to comment, do!
P.S. For more solutions to confusing word problems, see my 60 Quick Word Fixes.