The Manhattanville website says to take the #12 Bee-Line Bus.
http://mville.edu/AboutManhattanville/Directions.aspx#6Here is the link to the Westchester County Bee-Line Bus Timetables:
http://www.westchestergov.com/beelinebus/timetables.htmGo down towards the bottom to click on the link for the #12 Map and Timetable.
I don't know how many stops are on the bus ride before you get to Manhattanville or how long the bus ride would take, but I can't believe it would take more than 20 minutes or so.