Re: Conditional - polite request ... if you have (or had) time for a coffee?
I am a BrE speaker, and I would not say "Have you a car?" unless I were pretending to be a rather posh person from about 60 years ago.
I would use either:
Do you have a car?
Have you got a car?
I agree with the others that "I would like to ask you if you had/have time for a coffee" is overly complicated. Apart from anything else, if someone said that to me, I might sarcastically reply "OK. Go on then. Ask me if I have time for a coffee!" All you have said is that you would like to ask me a question. Technically, you haven't actually asked me if I have time for a coffee.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.