都…了【dōu…le】

都 before a time, an age or an amount, with 了 at the end, means "already" – and adds the speaker's feeling that it's a lot, or late, or more than expected.

Here 都 doesn't mean "all". It sits right in front of the time or number, and the 了 is required.

• × 都十二点，我们走吧 → 都十二点了，我们走吧

With 还 for a complaint

The most common frame adds a second half with 还: it's already this late, and you still haven't …

都 or 已经

已经…了 states a plain fact: "it's already twelve". 都…了 adds the feeling. The two can combine as 都已经…了 for extra weight.

It also goes before a verb of completion: 饭都凉了, "the food's gone cold already".