Work has already started on their designs but im not sure how far along that work is. The goal as of now is having the samples back by like 2033 or so. Perseverance, the current rover, has an undetermined amount of life left. Some rovers have made it 15 years. Other rovers made it about 5. But Curiosity is still going (11 years now I believe) and Perseverance is basically the same design but upgraded so hopefully should get another 10 years out of her easily.