How do I allow a couple extra weeks after issuign a 30 day notice

[Tony Vrolyk]

I have a SFH rental in Rockford IL and I issued a 30 notice to my tenants last month. That 30 days ends this month - Aug 31. They need a couple extra weeks to finalize their new housing which I am willing to do on a prorated basis. Is there any special procedure for this or can it be an oral agreement. My relationship with them is good so I don't anticipate them taking advantage. I just don't want to be in some weird legal bind where I have to start the 30 notice period over again or some such thing.

Thanks