A maintenance schedule was a list of what maintenance work needed to be done and when.
In 2369, Miles O'Brien apologized to Jaheel for being late in performing repairs to the Boslic's starship's antimatter flow converter, citing the fact that his crew was behind in their maintenance schedule. Jaheel didn't care about O'Brien's excuses, as his cargo of Tamen Sasheer had to reach Largo V before it began to spoil. O'Brien promised to send a repair crew to work on it by the end of the day, which Jaheel still felt wasn't good enough. (DS9: "Babel")
In 2373, Nog attempted to interest O'Brien with kayaking rather than recalibrating the EPS regulators, which he said he and Jake Sisko would do. He tempted O'Brien with the thought of "No interruptions, no maintenance schedules. Just you and the river." (DS9: "In the Cards")