At the announced or expected time, as in Her first baby arrived right on schedule. Originally alluding to published railroad timetables, this expression dates from the late 1800s.
Words nearby on schedule
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.