Maplestory "High Five" Private Showcase

Here's dropped item durations as of the live server patch around character level, then below, then above.
Spoilers: They last two minutes.

Except for Medals of Honor and event items.

I think that explains why the update notes specifically referred to "drops from monsters in your level range" (event items are classified that way) and said their duration was increased to 30 seconds. It used to be 15 or 20, if what we accidentally got last summer is any indication.