Pre approval block other bookings

I’ve had two enquiries re dates that overlap. The first guests stay would be half as long as the second. The first person I pre approved, then they didn’t book, so it expired, then he started to message again today. The 2nd wants to stay longer, I’ve sent a pre approval, and ticked the box that blocks the dates from others- but I’m not sure if that will work to stop the first one. Obviously, I’d rather have the second booking.

If the first guest didn’t book, that’s too bad. The second one who wants to book has precedence. #1 can’t book until #2 is cleared for the dates.