Only YOU know when you're at the end of your rope. I wouldn't recommend a 24-hour, or a 30-day, ultimatum if you're not ready to back it up.
Deliver the letter when you are truly "there."
I will say this: there's nothing that says that YOU have to allow him to go sow his oats with his recently-free friend. This should be about YOU at this point, and what YOU need, not what is convenient and fun for him.
