While they appear very similar, sometime, sometimes, and some time have slightly different meanings. Sometime means a vague point in time, and usually refers to a long amount of time. Sometimes means occasionally. Some time refers to a period of time.
Sometime refers to an unspecified point in time. It functions as an adverb, and is also synonymous with someday, one day, or sooner or later. Adverbs are words that describe verbs, adjectives, and other adverbs.
For example, in The Nightingale, Kristin Hannah uses sometime to refer to an indefinite time in the night: “As usual in the hot summer months, Sophie had kicked the coverlet to the floor sometime in the night.”
Sometime can also be an adjective that means occasional, but this use of the word is rare. For instance, one could say “He’s her sometime employee,” which implies that he only works for her on occasion.
Sometimes is a very common adverb that means occasionally or now and then. For instance, Kazuo Ishiguro uses sometimes in The Buried Giant: “She and Beatrice went on conferring in low voices, sometimes glancing towards the crowd, sometimes at Axl.”
Sometimes is an adverb of frequency, which is an adverb describing how often something happens. Some other adverbs of frequency are always, never, usually, and rarely. Sometimes is somewhat special in that it can go at the front, in the middle, or at the end of a sentence. For example, you can say “Sometimes he stays up late,” “He sometimes stays up late,” or “He stays up late sometimes.” The placement of other adverbs of frequency tends to be more restricted.
The two-word expression some time means a period of time or quite a while. Some is an adjective describing the noun time. For example, in Girl at War, Sara Novic uses some time to describe a period of time of an unknown length: “‘I think we need some time apart.’ When I saw the words reflected on his face I wished I hadn’t said them.”
In the following example from The Nightingale, Kristin Hannah uses some time to imply quite a while: “It looked like no one had been in this apartment for some time. Probably not since that day Papa had left to save Isabelle.” The implication is that a large amount of time had lapsed since anyone had been inside the apartment. Whereas Novic uses some time to mean an unspecified period of time, in this example Hannah uses some time to suggest a long time.