houmonyoteizikan ga kawarimasita.

It is a compound noun made of three parts:

• 訪問 = visit
• 予定 = plan / scheduled
• 時間 = time

So 訪問予定時間 means something like:

• the scheduled visit time
• the planned time of the visit
• the expected time for the visit

Japanese often combines nouns directly like this, without using words like of.

Because this is a noun compound.

In Japanese, it is very common to stack nouns together to make one long noun:

• 訪問予定時間
• literally: visit + planned + time

You could also say 訪問の予定時間, which is a little more expanded and easier to parse for learners, but the version without の is very natural in notices, business Japanese, and formal written language.

So:

• 訪問予定時間 = compact compound style
• 訪問の予定時間 = slightly more explicit

Both can work, but the compound form sounds efficient and natural in this kind of sentence.

が marks the thing that changed.

In this sentence, the thing that changed is:

• 訪問予定時間 = the scheduled visit time

So:

• 訪問予定時間が変わりました
• The scheduled visit time changed

A good way to think of it is:

• X が 変わりました = X changed

The focus is on what changed.

Yes, but the nuance changes.

• 訪問予定時間が変わりました
  = The scheduled visit time changed.
  This simply presents the change.

• 訪問予定時間は変わりました
  = As for the scheduled visit time, it changed.
  This can sound more contrastive, as if comparing it with something else.

For example, は might imply:

• the date did not change, but the time did
• other things stayed the same, but this changed

So が is the more neutral choice if you are just announcing the change.

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

Breakdown:

• dictionary form: 変わる = to change
• polite non-past: 変わります
• polite past: 変わりました

Even though it is past tense in Japanese, in English it often translates naturally as:

• has changed
• changed

That is because the change has already happened by the time the speaker says it.

Because 変わる is intransitive, while 変える is transitive.

• 変わる = something changes
• 変える = someone changes something

This sentence is about the time itself changing:

• 訪問予定時間が変わりました
• The scheduled visit time changed.

If you wanted to say that a person changed it, you would use 変える:

• 担当者が訪問予定時間を変えました
• The person in charge changed the scheduled visit time.

So here, 変わる fits because the sentence does not focus on who made the change.

Because Japanese often uses the past form to describe a completed change of state.

The idea is:

• before: one visit time was planned
• now: it is different
• therefore: it changed

So 変わりました means the change has already taken place.

In natural English, this often corresponds to:

• has changed

rather than a simple past like changed, depending on context.

Yes, it sounds neutral to formal.

It is especially natural in:

• business messages
• schedule notices
• appointment updates
• customer communication

The use of:

• the compound noun 訪問予定時間
• the polite verb 変わりました

makes it sound appropriate and professional.

In casual conversation, someone might say something simpler, such as:

• 訪問の時間が変わった
• 行く時間が変わった
• 予定の時間が変わった

By itself, 訪問 just means visit, so the direction is not clear from this word alone.

Depending on context, it could mean:

• your visit to someone
• someone’s visit to you
• a company visit
• a home visit
• a client visit

Japanese often leaves that kind of information to context.

So in this sentence, 訪問予定時間 just means the scheduled visit time, and you understand whose visit it is from the surrounding situation.

Quite a lot can be omitted in Japanese if the context is clear.

This sentence does not explicitly say:

• who is visiting
• who changed the time
• what the old time was
• what the new time is
• why it changed

It only says one thing clearly:

• the scheduled visit time changed

This is very normal in Japanese. If the surrounding context already makes the rest obvious, the sentence can stay short.

You can add the new result with に.

For example:

• 訪問予定時間が3時に変わりました。
• The scheduled visit time changed to 3:00.

You can also describe a change from one time to another:

• 訪問予定時間が2時から3時に変わりました。
• The scheduled visit time changed from 2:00 to 3:00.

So the basic pattern is:

• A が B に変わりました
• A changed to B

Both can relate to time, but they have slightly different feels.

• 時間 = time; can be broad and flexible
• 時刻 = a specific clock time; more precise and formal

So:

• 訪問予定時間 sounds natural and common
• 訪問予定時刻 would sound a bit more technical or precise

In many everyday and business contexts, 時間 is perfectly natural, even when referring to an appointment time.

It could, but it sounds less natural than 訪問予定時間が変わりました or 訪問の予定時間が変わりました.

Why?

Because 訪問予定 already works well as a unit meaning visit schedule / planned visit, so adding の between 予定 and 時間 can sound a little awkward.

More natural choices are:

• 訪問予定時間が変わりました
• 訪問の予定時間が変わりました

The original sentence is concise and very natural in formal contexts.

The structure is:

• 訪問予定時間 = noun phrase
• が = subject marker
• 変わりました = polite past verb

So the pattern is:

• [thing that changed] が 変わりました

Examples of the same pattern:

• 予定が変わりました。
  The plan changed.

• 時間が変わりました。
  The time changed.

• 担当者が変わりました。
  The person in charge changed.

This makes 訪問予定時間が変わりました a very typical and useful sentence pattern.