It's not a full sentence I don't think, and you could say "how many minutes" in a non interrogative sentence. "He wants to know how many minutes it takes."
but it's still a question, you literally cannot use an interrogative word such as how or 몇 without a question mark
you definitely can use interrogative words in non interrogative sentences. depending on context this could mean
"a few minutes" or "a few people" or it could mean
"how many minutes" or "how many people"