都 has two main meanings
都 primarily means "all, both, every": 我们都去 (we all go). That is the usage covered in ye-vs-dou. Separately, 都 means "already" in exclamatory contexts: 都这么晚了 (it is already this late!), 都六月了 (it is already June!). These two uses look identical on the page but function very differently. Context tells you which.
A: 我们都到了。B: 都九点了,怎么还没吃饭?
A: Wǒmen dōu dào le. B: Dōu jiǔ diǎn le, zěnme hái méi chī fàn?
A: We all arrived. B: It is already nine! Why have you not eaten?
已经 is the standard "already"
已经 pairs with 了 at the sentence end and marks completion: 我已经吃了 (I already ate), 她已经走了 (she has already gone). This is the default, neutral way to express "already" in Chinese. Learners should use 已经 by default and leave 都-as-already for when they want exclamation.
他已经准备好了,我们可以出发了。
Tā yǐjīng zhǔnbèi hǎo le, wǒmen kěyǐ chūfā le.
He is already ready; we can leave.
都 with time expressions = surprise
When 都 precedes a time expression with 了, it almost always means "already" with emotional emphasis. 都晚上了 (it is already night!), 都周五了 (it is already Friday!). The emotion is usually surprise at how much time has passed, sometimes with mild complaint ("I did not notice how late it got"). 已经 in these contexts is possible but loses the emotional punch.
Combining 都 and 已经
You can stack them for maximum emphasis: 都已经十点了 (it is already TEN O'CLOCK!). This is common in spoken Chinese for dramatic emphasis. The 都 amplifies surprise; the 已经 carries the "already" meaning. Pure 都十点了 works too; combining is just louder.
Position and the closing 了
已经 goes before the verb or adjective: 已经吃了 (already ate), 已经八点了 (it is already eight). The sentence-final 了 is typically required; dropping it makes the sentence incomplete. 都 as "already" behaves the same way positionally but has the extra emotional layer. Both require 了 at the end for completeness.