就要…了【jiùyào … le】

就要…了 says something is about to happen, and unlike 要…了 it accepts a stated time.

The time phrase is the reason to use it

要…了 and 快…了 both refuse a time phrase. 就要…了 is the one that takes one, and 就 carries the sense that the date is sooner than you might think.

Without a time phrase it means the same as 要…了, with a touch more urgency.

The time phrase goes in front

Before the subject or between subject and 就要 – both work, and it never goes at the end.

The 了 stays

tā他míng tiān明天jiù yào就要zǒu走 is not the pattern. Without the final 了 it reads as plain future, and the sense of something bearing down is gone.