sorosoro dekakenaito, siyakusyo no madoguti ga simatte simau.

そろそろ means something like soon, before long, or it’s about time.

In this sentence, it adds a feeling of timing and urgency:

• the right time to leave is arriving
• if you wait much longer, there may be a problem

So it is not just a neutral soon. It often suggests we should probably do this now.

出かける means to go out or to leave where you are and head somewhere.

That makes it a very natural choice here, because the speaker is talking about starting the trip:

• 出かける = leave the house / leave now / head out
• 行く = go

So 出かけないと focuses on getting going rather than just the destination.

A rough difference:

• 市役所に行かないと = we have to go to city hall
• 出かけないと = we have to leave now / get going

Here, 出かけないと is a conditional form.

It is made from:

• 出かけない = not go out / not leave
• と = if / when

So literally it means:

• if we don’t leave

That is important because learners often know Vないと as a shortened have to form, like:

• 行かないと = I have to go

But in this sentence, the next clause is stated explicitly:

• 出かけないと、 市役所の窓口が閉まってしまう
• If we don’t leave, the city hall counter will end up closing

So this is the real conditional if not, not just an omitted obligation phrase.

Yes, in context it does.

Even though the grammar is literally if we don’t leave, English often expresses this kind of sentence as:

• We’d better leave soon
• We need to get going soon
• If we don’t leave now, the city hall counter will close

So the urgency comes from the whole sentence, not from ないと by itself.

The subject is omitted, which is very common in Japanese.

From context, it is probably:

• I
• we
• or you and I

Japanese often leaves out subjects when they are obvious from the situation.

So 出かけないと does not explicitly say who is leaving, because the listener is expected to understand it from context.

の connects two nouns.

• 市役所 = city hall / municipal office
• 窓口 = service counter / reception desk / public service window

So 市役所の窓口 means:

• the city hall service counter
• the reception window at city hall

Here の works like:

• of
• at
• or a noun modifier in English

It shows that the 窓口 belongs to or is associated with 市役所.

Originally, yes, 窓 is window, but 窓口 is very often used for a service counter, public desk, or reception window.

In places like:

• city hall
• banks
• post offices
• train stations

窓口 usually means the place where you speak to staff and handle paperwork.

So here it does not necessarily mean a literal glass window. It means the public service counter.

が marks 窓口 as the grammatical subject of 閉まってしまう.

The thing that closes is the counter:

• 窓口が閉まる = the counter closes

This is very natural because 閉まる is an intransitive verb, meaning something closes on its own as a state change.

If you used は, the nuance would shift more toward making the counter the topic, but が is straightforward here because it marks what will close.

しまう adds nuance.

Base meaning:

• 閉まる = to close

With しまう:

• 閉まってしまう = to end up closing / to close completely / unfortunately close

In this sentence, しまう gives a feeling that the closing would be undesirable for the speaker:

• if we do not leave soon, the counter will close on us

So it adds a sense of:

• completion
• and often mild regret, inconvenience, or bad timing

If it were just 閉まる, it would sound more neutral.

This is the difference between an intransitive and a transitive verb.

• 閉まる = something closes
• 閉める = someone closes something

Here, the sentence is about the service counter becoming closed:

• 窓口が閉まる

If you wanted to say that the staff closes the counter, you would use 閉める:

• 職員が窓口を閉める = the staff closes the counter

So 閉まる is correct because the counter is the thing undergoing the change.

Plain form does not automatically mean rude. It often just means the speaker is talking casually.

In this sentence:

• 出かけないと
• 閉まってしまう

both are plain-style forms, which is natural in everyday conversation with family, friends, or people you are close to.

A more polite version could be:

• そろそろ出かけないと、市役所の窓口が閉まってしまいます。

So the sentence is casual, but not harsh.

The comma helps readability and shows a pause after the conditional part:

• そろそろ出かけないと、
• 市役所の窓口が閉まってしまう。

It separates:

1. the condition or warning
2. the result

In speech, there would usually be a slight pause there. In writing, the comma is helpful but not absolutely required in every case.