"We are leaving at nine at the latest."
Translation:Wir gehen spätestens um neun.
They say in the Tip the time statement can be right after the verb or right in front of it and here the front position in front of the sentence as I know as a native german speaker: "Spätestens gehen wir um neun" but that can also be a question better all "time" in front of the verb "Spätestens um neun gehen wir" and that is a clear statement because only the subject is after the verb than.
There are also accepted translations using the verb abfahren.
What was the entire sentence that you had in mind?
Edit: I see a report for Spätestens abfahren wir um neun from around the same time as your comment - was that your sentence?
That is not correct, because spätestens um neun has to stay together, and abfahren is a separable verb.
Spätestens um neun fahren wir ab is one possibility.
Because this sentence doesn't make any sense in German. The English word "to leave" has many different meanings, e.g.
a) leave something in a place as opposed to taking it with oneself
b) not doing something (let it be)
c) going away
The German word "lassen" has b) as its primary meaning. It can be used for a) as well, but "dalassen" or "zurücklassen" fits better then.
And it can never be used for c). Here you need a different word, e.g. "weggehen".
In addition it can have the meaning "to make someone do something", which the English "to leave" doesn't have. So the general message is: meanings of words don't match 1:1.