yīguì bùshì jīntiān chāixiè, jiùshì míngtiān chāixiè.

It is a fixed pattern meaning either...or....

So:

衣柜不是今天拆卸，就是明天拆卸。
= The wardrobe will be dismantled either today or tomorrow.

It does not mean a literal sequence like is not today, then is tomorrow. As a whole, it gives two alternatives.

They work as a pair in this pattern:

• 不是 A，就是 B
• meaning either A, or B

In this sentence:

• A = 今天拆卸
• B = 明天拆卸

So the speaker is saying there are two possible times, and one of them will happen.

Usually, yes. It often suggests that the speaker is not stating exactly which one is true yet, but believes it must be one of the two options.

Here, it sounds like:

• the wardrobe will definitely be dismantled soon
• but the exact day is still today or tomorrow

Depending on tone and context, it can also sound like the speaker is narrowing the possibilities down to just those two.

In Chinese, the first noun is often the topic or the thing being talked about, not necessarily the doer of the action.

Here, 衣柜 is the thing affected by 拆卸.

So Chinese can say:

• 衣柜不是今天拆卸，就是明天拆卸。

Even though in English we would naturally say:

• The wardrobe will be dismantled either today or tomorrow.

The wardrobe is not the agent, but it is the thing under discussion.

Chinese does not always need 被 to express something passive in English.

被 is often used when the speaker wants to explicitly mark a passive meaning, especially if the agent matters or if the event feels strongly affected, unexpected, or unpleasant.

Here, the sentence is simply about the schedule of dismantling the wardrobe, so 被 is unnecessary.

A version with 被 is possible in some contexts, but it would sound heavier:

• 衣柜不是今天被拆卸，就是明天被拆卸。

That is grammatical, but less natural for an ordinary scheduling statement.

It is repeated to keep the two halves parallel and clear:

• 今天拆卸
• 明天拆卸

Chinese often likes this kind of balance in paired structures.

In casual speech, if the meaning is obvious, speakers may sometimes omit repeated material. But repeating 拆卸 sounds clearer and more complete, especially in writing.

Also, a more natural everyday version would often use the shorter verb 拆:

• 衣柜不是今天拆，就是明天拆。

Both can mean dismantle / take apart, but they are not exactly the same in tone.

• 拆: common, everyday, conversational
• 拆卸: more formal, technical, or written

So for everyday speech, many people would say:

• 衣柜不是今天拆，就是明天拆。

The sentence with 拆卸 is understandable, but it sounds more formal.

In Chinese, time words usually come before the verb phrase.

So the normal order is:

• 今天拆卸
• 明天拆卸

This follows a very common Chinese pattern:

• time + verb
• for example: 今天去, 明天做, 昨天买

That is why the sentence is structured as:

• 不是今天拆卸，就是明天拆卸

not with the time word placed after the verb.

This is because of a tone change rule for 不.

Normally, 不 is fourth tone: bù.
But when it comes before another fourth-tone syllable, it changes to second tone: bú.

Since 是 is fourth tone, 不是 is pronounced:

• búshì

But it is still written as 不.

Not in the same way.

还是 is most commonly used in questions such as:

• 今天拆还是明天拆？
• Dismantle it today or tomorrow?

But in a statement meaning either...or..., 不是……就是…… is a better fit.

Another common statement pattern is:

• 要么今天拆，要么明天拆。

That also means either dismantle it today or dismantle it tomorrow.

So:

• 不是……就是…… = either...or...
• 还是 = often used for or in questions

Yes, it is grammatical and understandable, but it sounds a bit formal because of 拆卸.

A more natural everyday version would be:

• 衣柜不是今天拆，就是明天拆。

So the original sentence is fine, especially in more formal or written language, but many native speakers in daily conversation would probably choose 拆 instead of 拆卸.