Unless otherwise agreed, an offer to sell the thing to the holder of a right of first refusal must be accepted within ten days from the time it is received if the thing is movable, and within thirty days from that time if the thing is immovable.
Unless the grantor concludes a final sale, or a contract to sell, with a third person within six months, the right of first refusal subsists in the grantee who failed to exercise it when an offer was made to him.