The Phoenix navigation team at NASA's Jet Propulsion Laboratory, Pasadena, Calif., made that recommendation after assessing the trajectory this week and mission management accepted the recommendation late Thursday.
Phoenix has performed three flight path correction maneuvers since its Aug. 4, 2007, launch. Besides the May 17 one, the final opportunity for adjusting the course to hit the targeted landing area will be in the final 24 hours before landing.
The first possible confirmation time for the spacecraft's landing on May 25 will be at 4:53 p.m. Pacific Daylight Time. The event would have happened 15 minutes and 20 seconds earlier on Mars, and then radio signals traveling at the speed of light will take 15 minutes and 20 seconds to cross the distance from Mars to Earth on that day.
Source: NASA