一。時間（じかん・jikan）時間があるなら / if you have time 2時間 / 2 hours (Here jikan means a period of time.) 二。時（とき・toki）悲しいとき / when I'm sad (Here toki means when, a time point. It's used as a preposition.) 三。いつ（itsu）いつ卒業ですか？ / When will you graduate? (Here itsu also means when. But it's used as an interrogative adverb.)

when you eat,you use chopsticks almost,right? when = toki, when do you eat the chocolate ? when = itu Do you have a time? time= jikan