This Saturday if you have free time, I would like to invite you to come have lunch together at the hotel, but if you're not busy it doesn't matter because I am meeting a friend for lunch at noon only.
Saturday, if you have time, I would like to invite you to come to lunch with me at the hotel. But if you are busy, not because I meet a friend for lunch only.
This Saturday if you have free time I'd like to invite you to have lunch together at the hotel. But if you are busy fine because I meet a friend for lunch.