Generally, sometime is written as one word with no space: we will go out for dinner sometime. Sometime is an adverb and means ‘at one time or another’.
If using some as an adjective to modify time, meaning 'a short time', 'a considerable amount of time' or 'an indefinite time', then it should be written as two words: it has been some time since we updated the user interface. Some time is correct when a preposition precedes it or a helping word follows it: I have been meaning to call you for some time. We last spoke some time ago. Other phrases can be substituted for some time (e.g. a short time, a long time), but sometime cannot be replaced, e.g.: the audit will take place sometime in May.
Sometimes means ‘occasionally or now and then’: I sometimes take my dog for a run on the beach.