It really depends on the person.
Some people you can say you have a question and it'll occupy their mind not knowing what it is.
Some people can happily just wait until the actual question comes through, but once it does that's the thing they're thinking of.
"Do you have a minute" and "Do you have a minute, I've an issue with X" have problems, but for different people.
Colleague: "Hey, do you have a minute to get on a call?"
Me: "Maybe. What is it about?"
Colleague: "I was looking at X and had a question."
Me: "I can meet with ..."
Why not cut the chase here and start with "I was looking at X and had a question, do you have a minute?"
I almost never do have a minute without notice but I'm happy to find a few minutes to give people. I don't like having to play this 21-questions game with people to find out what they need, though. It really irks me.