kinmuzikan ga kawarimasita.

It is read:

きんむじかん が かわりました。
Kinmu jikan ga kawarimashita.

• 勤務時間（きんむじかん） = working hours / hours of duty / office hours
• 変わりました（かわりました） = changed

勤務時間 is a compound noun:

• 勤務 = service, duty, work
• 時間 = time, hours

Together, 勤務時間 means working hours, duty hours, or office hours, depending on context.

In many real situations, it refers to:

• the hours employees are expected to work
• a schedule such as 9:00–17:00
• a company's official workday hours

が marks 勤務時間 as the thing that changed.

So the structure is basically:

• 勤務時間 = working hours
• が = subject marker
• 変わりました = changed

So the sentence means:

The working hours changed.

With verbs like 変わる meaning to change, the thing that undergoes the change is often marked with が.

This is a very common question because Japanese has both an intransitive and a transitive version here.

• 変わる = to change
  something changes by itself / is changed
• 変える = to change something
  someone changes something

This sentence uses 変わりました, so it focuses on the working hours as something that changed.

• 勤務時間が変わりました。 = The working hours changed.
• 会社が勤務時間を変えました。 = The company changed the working hours.

So the original sentence does not say who changed them. It just says that the hours changed.

In Japanese, the past form often shows that the change has already happened.

So 変わりました can naturally mean:

• changed
• has changed
• have changed

depending on context.

It does not necessarily mean only a finished event in the distant past. It often means:

The change has taken place.

That is why this sentence is very natural in announcements.

Yes. 変わりました is the polite -ます past form of 変わる.

Levels of style:

• 勤務時間が変わりました。 = polite
• 勤務時間が変わった。 = casual / plain
• 勤務時間が変更になりました。 = more formal, announcement-like

So the sentence is polite and very normal in workplace communication.

Yes, は is also possible, but the nuance changes.

• 勤務時間が変わりました。
  Focuses on the fact that the working hours changed.
  It sounds straightforward and neutral.

• 勤務時間は変わりました。
  Puts 勤務時間 on topic and can imply contrast, such as:
  As for the working hours, those changed
  maybe while something else did not.

So if you are simply announcing the change, が is very natural.

The sentence does not explicitly say.

Japanese often leaves that kind of information to context. Depending on the situation, it could mean:

• our working hours changed
• the employees' working hours changed
• your work schedule changed
• the company's office hours changed

If the speaker wanted to be more specific, they could say something like:

• 社員の勤務時間が変わりました。 = The employees' working hours changed.
• 当社の勤務時間が変わりました。 = Our company's working hours changed.

Japanese nouns usually do not mark singular vs. plural the way English does.

So 勤務時間 can mean:

• working hours
• work schedule
• sometimes even working time

In practice, English often translates it as working hours, even though the Japanese noun itself does not explicitly show plural.

Japanese normally does not use spaces between words.

So in natural writing, you would usually see:

勤務時間が変わりました。

Spaces are often added in textbooks or beginner materials to make the grammar easier to see.

Yes, it is natural.

It sounds like something you might hear in:

• a workplace notice
• an HR announcement
• a school or company schedule update

Depending on the level of formality, other natural versions are:

• 勤務時間が変わりました。 = The working hours changed.
• 勤務時間を変更しました。 = We changed the working hours.
• 勤務時間が変更になりました。 = The working hours have been changed. / There has been a change in working hours.

The original sentence is simple, polite, and natural.

Yes. Even though 変わる is intransitive, in real life people often understand that someone made the change.

The sentence simply does not focus on the person or organization that did it. It focuses on the result:

The working hours are now different.

This is very common in Japanese, especially in notices and announcements, where the result matters more than the actor.

The structure is:

noun + が + intransitive verb

More specifically:

• 勤務時間 = noun
• が = subject marker
• 変わりました = polite past of an intransitive verb

So the sentence pattern is:

X が 変わりました
= X changed

You can use the same pattern with many other nouns:

• 予定が変わりました。 = The plans changed.
• 時間が変わりました。 = The time changed.
• 場所が変わりました。 = The location changed.