Full-Price Offer

I assume your prospective buyer is offering all cash? If the offer is contingent on obtaining financing, it doesn't seem likely that could be done in 30 days. At any rate, you can certainly make a counter-offer stipulating a closing date you'd prefer. Of course, when you make a counter, the other party is no longer bound and could decide to drop the matter altogether. It's your personal decision, whether receiving full price for sure is worth it to you, or whether you will take a chance by countering it.