Irregular
Temporary, Provisional
noun, の adjective
You look to the time, because something irregular seems to be happening outside the normal schedule.
臨時 highlights something out of the ordinary, like 臨時の仕事 (temporary job) or 臨時休業 (unscheduled closure). It can also sometimes mean "extra," but only in a special, irregular sense, like 臨時ボーナス (extra bonus).
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
台風の影響で、臨時休校になった。
School was temporarily closed due to the typhoon.
臨時ニュースが入りました。
We have breaking news.
今日はイベントのための臨時バスが運行されています。
A temporary bus service is running today for the event.
臨時収入があったので、ハーゲンダッツを買っちゃいました。
I came into some extra income, so I bought myself some Häagen-Dazs.