Corrected entry: When Mark is communicating with the scientists at any given point while he is on Mars, they can communicate back and forth within seconds. In reality, it would take between 4.3-21 minutes for a message to reach Mark and vice versa.
bobthedancingdonut
18th Nov 2015
Correction: They explain in the movie that it takes 30 minutes between communications. Obviously cut out due to not making people wait between every sentence.