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.