Transmissions from Mars to Earth and visa versa happen at the speed of light. However, Mars is sometimes near Earth and sometimes on the other side of the sun. Therefore, depending on where Mars is in relation to Earth in our orbit around the sun, transmission times change from 4 minutes to 24 minutes. If Mars is close to Earth in orbit around the sun it’s 4 minutes. If Mars is on the other side of the sun from Earth in our orbit, it’s about 24 minutes.