maybe another time
1. A polite way to refuse an invitation. A: "Would you like to go out for dinner tonight?" B: "Sorry, maybe another time. I have a lot of work I need to catch up on."
2. A polite response to such a refusal. A: "I wish I could come to your house for dinner, but I told my sister I would babysit for her." B: "That's all right, maybe another time."