The correct response is:
The acting president may retain office for a maximum of 10 years as long as there are less than two years left in the previous president’s term.
This is based on the 22nd Amendment to the U.S. Constitution, which limits a person to being elected as President for a maximum of two terms (four years each) or a total of 10 years if they assume the presidency via succession (e.g., if a vice president takes over the presidency) with the stipulation that they serve less than two years of the predecessor's term. If they serve more than that, it counts as a full term.