Two-thirty on the analog clock set, used the same interchangeable way as its siblings — as visual shorthand for 'time' in general rather than the specific half hour. It's one of the emoji least likely to appear in anyone's frequently-used tray, since typing an actual number ('2:30') is almost always faster and clearer.
Keywords: 2, 2:30, 30, clock, thirty, time, two, two-thirty