Is 多早晚 wrong or right In that site it says 多早晚 means "When". I asked a friend from Singapore, she told me that no one uses that, and it's a mistake. I would like to know if you use it, and in which context.

https://chinese.yabla.com/chinese-english-pinyin-dictionary.php?define=zao+wan
Looks like classical Chinese.
zdic

◎ 多早晚 duōzǎowǎn
[when] 多咱,什么时候(“多咱”来于“多早晚”)

多早晚
什麼時候。紅樓夢．第十四回：「我且問你，你們這夜書多早晚纔念呢？」或作「多早」、「多咱」、「多咱晚」、「多偺」、「多喒」。
甚晚、很晚。

百度百科

中文名 多早晚
外文名 Much sooner or later
性质 词语
来源 红楼梦
多早晚 duōzǎowǎn [when] 多咱，什么时候(“多咱”来于“多早晚”)
《红楼梦》第六四回：“黛玉道：‘可是你没的说了！好好的，我多早晚又伤心了？’”
茅盾《霜叶红似二月花》：“我早就想过，多早晚，我们村子里一人一股香，大家上县里去，一步一拜，打伙儿跪在王伯申大门前，求他高抬贵手。”

As the encyclopedia entry mentions 多咱 comes from 多早晚 and is in common usage in Northern China. You might be hard pressed to find usage of 多早晚 outside of 红楼梦 though.