zikan ga aru nara, hiru mo yoru mo naikensitara dou desu ka.

In 時間があるなら, が marks 時間 as the thing that exists: if there is time / if you have time.

Using は is not impossible in other contexts, but 時間がある is the most natural basic expression for to have time. Japanese often uses X がある for possession or availability of something:

• お金がある = to have money
• 時間がある = to have time
• 予定がある = to have plans

So here, 時間があるなら simply means if you have time.

なら means if, but it often has the nuance of if that is the case or if so.

So:

• 時間があるなら = if you have time
• more literally: if it’s the case that you have time

Compared with some other conditionals, なら often sounds like the speaker is responding to a situation already being considered. For example, if someone says they are free, the speaker might reply:

• 時間があるなら、昼も夜も内見したらどうですか。

That gives it a natural well, if you do have time, then... feeling.

Because ある is part of the condition: if you have time. In Japanese, the plain non-past form is commonly used before なら.

So:

• 時間がある = you have time
• 時間があるなら = if you have time

It does not mean only present tense in a narrow English sense. Japanese non-past often covers present and future depending on context. Here it means something like:

• if you have time (available)
• if you will have time

The repeated も means both ... and ... or ... as well as ....

So:

• 昼も夜も = both during the day and at night

Using も after each item emphasizes that both times are included. It is similar to:

• 朝も夜も働く = work morning and night
• 日本語も英語も話せる = can speak both Japanese and English

In your sentence, the idea is: don’t just see it at one time of day; see it in both conditions.

It is broader. 昼 here usually means daytime rather than strictly noon.

So:

• 昼 = daytime / during the day
• 夜 = nighttime / at night

In a property-viewing context, this makes sense because a place can feel different in the daytime and at night. The sentence is suggesting checking both.

内見 is a noun meaning something like an interior viewing or a property viewing, especially in real estate. It is commonly used as a suru-verb.

So:

• 内見 = a viewing
• 内見する = to view a property / to inspect the inside

In the sentence, 内見したら comes from 内見する:

• 内見する → 内見したら

So yes, it is a noun that can function as a verb with する.

This is a very common suggestion pattern:

• V-たらどうですか = How about doing ...? / Why don’t you do ...?

So:

• 内見したらどうですか = How about viewing it?
• more naturally here: Why not do a viewing?

The たら form here does not literally mean past. In this pattern, it is part of a fixed suggestion expression.

Other examples:

• 少し休んだらどうですか。 = Why don’t you rest a little?
• 先生に聞いたらどうですか。 = Why don’t you ask the teacher?

So the full sentence is suggesting a course of action.

Both can be used to make suggestions.

• V-たらどうですか
• V-てはどうですか

Both mean roughly Why don’t you ...? / How about ...?

So these are both possible:

• 内見したらどうですか。
• 内見してはどうですか。

The たらどうですか version is very common in everyday conversation and often feels a bit more direct and natural in speech. てはどうですか can sound a bit more formal or written, depending on context.

The difference is small here; the main point is that both are suggestion patterns.

This is normal in Japanese. The sentence mixes a plain-form verb before a grammar pattern with a polite ending.

• 内見したら is the plain conditional form
• どうですか is the polite ending

This happens all the time because many grammar structures require the plain form before them, even in polite speech.

For example:

• 行ったらどうですか。 = Why don’t you go?
• 食べるなら、早くしてください。 = If you’re going to eat, please do it soon.

So the sentence is still polite overall because it ends with ですか.

Yes, the object is omitted, which is very common in Japanese.

From context, 内見する usually means to view a property / apartment / house / room. Japanese often leaves out obvious objects when the situation makes them clear.

So even though the sentence does not explicitly say:

• その物件を内見する = to view that property

the listener can understand it from context.

This is one reason Japanese can sound shorter or less explicit than English.

It sounds like a reasonable, practical suggestion rather than a strong command.

• 時間があるなら softens it: if you have time
• 内見したらどうですか is a suggestion: why not ...?

So the tone is something like:

• If you have the time, why not view it both during the day and at night?

It suggests that seeing the property at different times could help you make a better judgment. It is helpful advice, not an order.

It is fine if the context is already clear, especially in a conversation about apartments or houses.

In Japanese, once the topic is established, it is very natural to omit words like:

• その部屋を
• その家を
• その物件を

So if two people are already discussing a specific place, 昼も夜も内見したらどうですか。 sounds natural.

If there were no context at all, then it might feel incomplete, and the speaker would probably specify what should be viewed.