Разгрузка начнётся завтра, разве что грузовой фургон приедет сегодня.

Here разве что introduces an exception to the main statement.

The basic idea is:

• Разгрузка начнётся завтра = the default expectation
• разве что грузовой фургон приедет сегодня = the one thing that could change that

In natural English, this often corresponds to:

• unless
• except maybe if
• unless, of course,

So the sentence means something like: unloading will start tomorrow, unless the cargo van arrives today.

Начнётся is the future form of начаться, which means to begin / to start as an intransitive verb.

That fits разгрузка well, because the sentence means the unloading will begin, not someone will start the unloading.

Compare:

• Разгрузка начнётся завтра = the unloading will begin tomorrow
• Они начнут разгрузку завтра = they will start the unloading tomorrow

Why not будет начинаться?

Because Russian usually uses the perfective future for a single event that will happen once in the future. The beginning of unloading is a one-time event, so начнётся is the natural choice.

The -ся here is part of the verb начаться.

Russian often uses a reflexive-looking form for events that begin on their own or are presented without an active starter. So:

• начать = to start something
• начаться = to begin

Compare:

• Они начнут работу = they will start the work
• Работа начнётся = the work will begin

So разгрузка начнётся is the normal way to say the unloading will begin.

Разгрузка is in the nominative case.

It is the subject of начнётся:

• разгрузка = unloading
• начнётся = will begin

So literally, the structure is unloading will-begin tomorrow.

Грузовой фургон is also in the nominative case, because it is the subject of приедет.

Breakdown:

• грузовой = cargo / delivery / freight-related
• фургон = van
• приедет = will arrive / will come by vehicle

So грузовой фургон приедет сегодня means the cargo van will arrive today.

Also note that грузовой agrees with фургон:

• masculine
• singular
• nominative

Приедет is used because the arrival is by vehicle.

Russian distinguishes between kinds of motion:

• прийти = to come on foot
• приехать = to come by transport

Since we are talking about a van, приедет is the correct verb.

Because сегодня and завтра are adverbs, not nouns.

Russian uses them directly for time:

• сегодня = today
• завтра = tomorrow

So:

• приедет сегодня = will arrive today
• начнётся завтра = will begin tomorrow

No preposition is needed.

No. The arrival today is presented as a possibility, not a fact.

That is exactly what разве что suggests: the main plan is that unloading starts tomorrow, and the van arriving today is only an exception that might change that.

So the tone is something like:

• probably tomorrow
• unless the van happens to arrive today

The comma separates the main statement from the exception clause.

Structure:

• main statement: Разгрузка начнётся завтра
• exception: разве что грузовой фургон приедет сегодня

This punctuation is standard and helps show that the second part modifies the first as an exception or limitation.

Not exactly.

Грузовой фургон literally means something like:

• cargo van
• delivery van
• light freight van

It usually suggests a smaller cargo vehicle than грузовик, which is a more general word for truck.

So in context, English might translate it differently depending on the situation, but cargo van or delivery van is the most literal match.

Yes. Russian word order is flexible, though the original order is neutral and natural.

The sentence as written:

• Разгрузка начнётся завтра, разве что грузовой фургон приедет сегодня.

This sounds like a normal, straightforward statement.

If you changed the order, you could shift emphasis. For example:

• Разгрузка завтра начнётся... puts a little more focus on tomorrow
• ...разве что сегодня приедет грузовой фургон puts more focus on today

But the original version is the most neutral and natural for ordinary speech or writing.

Yes, but it would be a different phrasing.

For example:

• Разгрузка начнётся завтра, если только грузовой фургон не приедет сегодня.

That also means roughly unloading will start tomorrow, unless the cargo van arrives today.

The version with разве что is shorter and often feels a bit more conversational or idiomatic in this kind of statement of exception.