Do people still use the term "昨晚“？ Is it very 口语？ Could it be used when writing a diary?
Example sentence 昨晚十点我从我的家开始开到纽约。
-
1Feel free to use it wherever you can use "last night". – Stan Oct 6 '14 at 6:36
昨晚 is a very common word. You can use it in both oral and written Chinese.
昨 here is used as adjective. It means yesterday. However 昨 still has other meanings. 昨 also means past days.
昨晚 = 昨天夜里 , 昨夜
You can use it in all situation.
Reference : http://www.zdic.net/z/1b/js/6628.htm
I would say that 昨晚 is not terribly literary but perfectly acceptable in most situations, both spoken and written. In particular, it fits perfectly in a diary entry.
昨夜 is a more dignified, literary version that would be common in literary writing but out of place in the spoken language. It is also the expression for "yesterday night" in the classical literary language, as in this poem by Li Houzhu, the "Poet King" of Southern Tang:
虞美人
春花秋月何時了，往事知多少？
小樓昨夜又東風，故國不堪回首月明中。雕闌玉砌應猶在，只是朱顏改。
問君能有幾多愁？恰似一江春水向東流。
Yeah, 昨晚 is the short version of 昨天晚上, it is very commonly used still
