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.