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.
I'm from the northeast of China. At first, I'm surprised to learn that, "多早晚" means "when". Finally I find out that, in my home town, people usually pronounce it as "多咱"（duō zǎn）to mean "when" , and I've never known the exactly written characters of that phrase till I see this question.
And I should say, I have NEVER saw this phrase in formal written Chinese. So avoid the use of this phrase in written Chinese, and also in spoken Chinese because native Chinese listeners from other parts of China may not understand the phrase.
This phrase can be used in informal situations (seems only in the northeast? maybe ), for example:
The two sentences are both ok in daily spoken situations, which mean "when will we go".
Looks like classical Chinese.
◎ 多早晚 duōzǎowǎn
外文名 Much sooner or later
多早晚 duōzǎowǎn [when] 多咱，什么时候(“多咱”来于“多早晚”)
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.