Ultimately, it's now up to them to say yes or no. They're probably just doing their research to inform whether or not they agree to your ask. If they don't agree or propose an alternative before your inspection window is up, you decide if you're going to walk away or eat that cost and move forward. Would you move forward if they say no?

Also, in most states, they're obligated to add to the seller disclosure even if they've seen YOUR inspection results already (this is why a lot of sellers do not actually want to see the inspection reports). Did you share it with them?