First, there were zero timetable changes during the month of February.
For March, the timetable updates are related to some significant timing changes along the Northeast Corridor due to various construction projects. And in the West, the long distance trains that touch Arizona will get new timetables because of that state's non-participation in Daylight Savings Time, which begins March 11th.
The following timetables change effective Saturday, March 10th:
Northeast Corridor (New York-Washington)
Northeast Corridor (New England-Washington)
Northeast Corridor (Northeast-Virginia)
Related thread: Service advisory for Acela Express & Northeast Regional
The following timetables change effective Sunday, March 11th:
And finally, a System Timetable dated March, 2018.