It appears that the first manned Crew Dragon flight to ISS may be extended due to there being only one US astronaut there.
NASA is also trying to determine how long Dragon's first crewed mission will take. Initially, the space agency had planned to dock the capsule to the space station for about a week before Hurley and Behnken returned to Earth. Now it wants to extend that mission so the pair of astronauts can do more work on orbit.
Later this spring, after NASA astronauts Jessica Meir and Drew Morgan return to Earth, only Chris Cassidy will remain on board the station. NASA would like to minimize the time Cassidy remains the lone US astronaut on board the orbiting laboratory, so there is discussion of extending Hurley and Behnken's mission to six weeks, or even three months.
Soyuz has a 200-day limit. Is the maximum time on orbit known for Crew Dragon?