Any time is a two-word noun phrase: any describes the noun time. Use it when referring to an unspecified point or amount of time. It is also the standard form after a preposition such as at.
- Is there any time left before the store closes?
- You can submit the form at any time.
Anytime is usually an adverb meaning “whenever” or “at any time.” It often tells us when an action can happen.
- We can meet anytime next week.
- Stop by anytime you are in the neighborhood.
Sometimes both forms are possible when the phrase means “whenever.” For example, both “You may visit any time” and “You may visit anytime” are widely used. The two-word version treats time as a noun, while the one-word version functions as an adverb.
The forms are not always interchangeable. After a preposition, keep the space: write “at any time,” not “at anytime.” The two-word form is also necessary when discussing an amount of time, as in “I do not have any time to cook.”
If you are unsure, check what the words are doing in the sentence. Choose any time when time is a noun or follows a preposition. Choose anytime when you can naturally replace it with whenever.