hanamaru
Say how many hours something takes
Number + じかん is hours: いちじかん, one hour. ぐらい after it makes it approximate: にじかんぐらい, about two hours. Ten o'clock is じゅうじ, ten hours is じゅうじかん.
JLPTN5
number + じかん (hours) · 〜ぐらい (about)~ jikan · ~ gurai
Clock time and length are two different words. じ is the clock time: さんじ, three o'clock. じかん is the length: さんじかん, three hours. Minutes as a length use the same ふん as the clock: さんじゅっぷん, thirty minutes; half an hour is さんじゅっぷん or はんじかん — not はん.
ぐらい after an amount means “about”: いちじかんぐらい, about an hour; さんびゃくえんぐらい, about three hundred yen. The question is どのぐらい: えきまで どのぐらい かかりますか — how long does it take to the station? The answer: あるいて じゅっぷんぐらいです. The verb for taking time is かかります.