Rover client hasn’t confirmed booking and another client is waiting. What would you do?

I could use some advice.
I got a Rover request first for a Golden Retriever puppy from July 11–15. Before anything was officially booked, we scheduled a meet and greet.
After that, my grandma’s friend’s daughter reached out asking if I’d be available to watch her two small dogs (a Shih Tzu mix and a Lhasa Apso) from July 11–18. I told her I’d let her know after I met the Rover client since that request came in first.
I had the meet and greet today and it went really well. They seemed like they wanted to move forward, and I already confirmed the booking on my end, but I’m still waiting for the owner to accept it.
So now I’m kind of stuck. I don’t want to tell the second client I’m unavailable if the Rover booking falls through, but I also don’t want to keep her waiting if she needs to find someone else.
What would you do? How long would you wait before following up or moving on?