После маникюра мастер сказала, что лак будет держаться дольше, если не мочить ногти два часа.

Because после always takes the genitive case. The noun маникюр changes to маникюра in the genitive singular.

A useful thing to memorize is:

• после + genitive = after
• до + genitive = before / until
• без + genitive = without

So после маникюра means after the manicure.

Yes, мастер is grammatically a masculine noun, but in Russian it is often used for a person of either sex, especially for professions such as a technician, specialist, or craftsperson.

The past-tense verb shows the real person’s gender:

• мастер сказал = the specialist was male
• мастер сказала = the specialist was female

So here the nail technician is a woman. This is common in modern Russian speech.

Not in the English sense of master. In this context, мастер means something like:

• specialist
• technician
• professional
• nail technician

In beauty-service contexts, Russians very often say мастер for the person who does nails, hair, brows, and so on.

Here что means that and introduces a subordinate clause:

• мастер сказала, что... = the technician said that...

This is a very common structure in Russian:

• Я знаю, что... = I know that...
• Он сказал, что... = He said that...

That is also why there is a comma before что.

Literally, держаться means to hold on, to stay, or to remain in place. With things like nail polish, makeup, hair color, or perfume, it often means to last or to wear well.

So:

• лак держится = the polish lasts / stays on
• лак будет держаться дольше = the polish will last longer

Even though English uses last, Russian uses a verb built from the idea of staying on.

Because держаться is an imperfective verb. In Russian, the future of an imperfective verb is formed with быть + infinitive:

• будет держаться

This is sometimes called the compound future.

Russian uses the imperfective here because the focus is on the ongoing result or duration: how long the polish continues to stay on.

Дольше is the comparative form of долго, meaning longer.

So:

• долго = for a long time
• дольше = longer

Russian usually prefers this short comparative form rather than something like более долго. So будет держаться дольше is the normal, natural way to say will last longer.

Russian often uses the infinitive to give general advice, instructions, or impersonal recommendations.

So если не мочить ногти два часа means:

• if you do not get your nails wet for two hours
• more literally, if not to wet the nails for two hours

The subject is understood as a general you. This is very natural in spoken Russian, especially when giving practical advice.

They are different:

• мочить = to wet, to get wet, to soak
• мыть = to wash

Here the technician is not only saying don’t wash your nails. She means don’t let them get wet at all. Even brief contact with water is the problem.

So не мочить ногти is broader than не мыть ногти.

Ногти is the plural direct object of мочить.

The basic forms are:

• singular: ноготь = nail
• plural: ногти = nails

Here it means nails as the thing being wetted, so it is in the accusative plural. For inanimate plural nouns, the accusative usually looks the same as the nominative, so ногти stays ногти.

Because after the numbers 2, 3, 4, Russian normally uses the noun in a form that looks like the genitive singular:

• два часа
• три часа
• четыре часа

After 5 and higher, Russian usually uses the genitive plural:

• пять часов
• шесть часов

So два часа is the correct form here.

Russian often expresses duration without a separate word meaning for.

So:

• не мочить ногти два часа = not get the nails wet for two hours

This is very normal Russian. The time expression stands on its own, and the meaning of duration is understood from context.

Because если introduces a subordinate clause:

• если не мочить ногти два часа = if you do not get your nails wet for two hours

In Russian, clauses introduced by words like что, если, когда, потому что are normally separated by commas.

So the commas before что and если are both required.

Usually, no. In standard Russian punctuation, you would normally write:

После маникюра мастер сказала, что лак будет держаться дольше, если не мочить ногти два часа.

The opening phrase после маникюра is just a normal adverbial phrase, and it usually does not need a comma after it. The other two commas are correct and necessary.