It is never necessary to join 'some' and 'time' together to make an adverb 'sometime'. Some people join them together and invent rules about when to use this word, but it is completely necessary. If you leave them as two separate words, it will always be correct. For example:
We must meet up for a drink some time.
Why don't you come over and visit us some time?
Let's go and watch a movie some time.
Forget about 'sometime'. You don't need it.