Hi Overcomer,
Isn't it frustrating to be pulled into someone's unhealthy ecology? I say ecology because it's behavior that affects others. "Aware" or self-aware or other-aware people do ecology checks to see how their behavior will affect others - then proceed with caution.
I think it's totally okay to speak your boundary. "I need at least 48 hours to work things into my schedule, barring emergencies, of course! Have a lovely time!"
Don't allow them to pull you in to the drama. If they complain about you, and you get wind of it, simply repeat your mantra. "I need 48 hours to work things into my schedule, barring emergencies of course!" Smile and breeze away. Certain and in control. They will respect you for it. Don't back down or be defensive or make excuses for your behavior.
I'm with ya'.....
Dandylife