which county is this property in? and are you the seller or the buyer?
If you're the seller, you have to pay as soon as possible, of course. However, there is some time, unless an investor purchased your tax certificate.
If you're the buyer, when you close, the title co. or the Lender will pay off the property taxes from the proceeds of the sale, before the remainder funds are wired to the seller or the seller's lender.
It's good to have an attorney to protect your interests in a short sale or an REO (bank-owned).