Duration of time ( Genki I Chapter 4)

いちじかん

The duration of an activity is expressed with a bare noun, like いちじかん. Such nouns are not followed by particles and usually appear immediately before the verb. Approximate measurements can be expressed using ぐらい after ~じかん.

メアリーさんはそこでたけしさんをいちじかんまちました。

Mary waited for Takeshi there for an hour.

わたしはきのうにほんごをさんじかんぐらいべんきょうしました。

I studied Japanese for about three hours yestereday.