Unless the parties provide otherwise by written agreement, within sixty days after the oil and gas developer received the notification of claim specified in section five of this article, the oil and gas developer shall either make an offer of settlement to the surface owner seeking compensation, or reject the claim. The surface owner may accept or reject any offer so made: Provided, That the oil and gas developer may make a final offer within seventy-five days after receiving the notification of claim specified in section five of this article.