I saw “anytime” used where “any time” was required in a technical document.

Problem:
“Anytime” and “any time” are not synonyms.

Explanation:
“Anytime” is an adjective. “Any time” is an adverbial phrase.

It’s an anytime event to have Bill Clinton visit our donut shop. is an example of the proper use of “anytime”. The adjective “anytime” tells the reader/listener the what type of event it is to have Bill Clinton visit the writer/speaker’s donut shop.

Getting stuck in the longest line happens any time that I try to pick the shortest line at the grocery store. is an example of the proper use of “any time”. The adverbial phrase “any time” tells the reader/listener when the writer/speaker gets stuck in the longest line.

Solution:
Use “anytime” when you are modifying a noun; use “any time” when you are modifying a verb.