Раз завтра у нас выходной, то можно лечь спать попозже.

Here раз means since / as / given that, not once.

So:

• Раз завтра у нас выходной... = Since tomorrow is our day off...

This use of раз is common in spoken and informal written Russian. It introduces a reason.

Compare:

• Я видел его один раз. = I saw him once.
• Раз ты устал, иди домой. = Since you’re tired, go home.

So the meaning depends on context.

То helps complete the logical pattern раз ..., то ..., which is similar to:

• if/since ..., then ...

In this sentence:

• Раз завтра у нас выходной, то можно лечь спать попозже.

Literally: Since tomorrow is a day off for us, then it’s possible to go to bed later.

A few important points:

• То is often optional
• It makes the sentence sound a bit more structured or emphatic
• In everyday speech, people may omit it

For example:

• Раз завтра у нас выходной, можно лечь спать попозже.

This is also completely natural.

This is a very common Russian pattern.

• у нас literally means by us / at our place / for us
• выходной means day off

So:

• Завтра у нас выходной = Tomorrow we have a day off

Russian often uses у + genitive to express possession or situations affecting someone.

Compare:

• У меня машина. = I have a car
• У нас урок. = We have a lesson
• У него выходной. = He has a day off

So even though it looks different from English, it is a standard Russian way to say have.

Because выходной can function on its own as a noun-like word meaning a day off.

Originally it is an adjective:

• выходной день = day off

But very often день is omitted because it is obvious from context:

• У меня сегодня выходной. = I’m off today / I have today off
• Завтра у нас выходной. = Tomorrow we have a day off

This is extremely common and natural.

In this sentence, завтра is not being used as a noun in a case form. It is an adverb meaning tomorrow.

So:

• завтра = tomorrow
• no case ending is involved here

It simply sets the time:

• Раз завтра у нас выходной... = Since tomorrow we have a day off...

Russian also has nouns related to time that do take cases, but завтра here is just an adverb.

Можно is an impersonal word meaning something like:

• it is possible
• it is allowed
• one can

So:

• можно лечь спать попозже = it’s possible to go to bed later / we can go to bed later

Russian often leaves the subject unspoken when the meaning is general or obvious from context.

Compare:

• Здесь можно курить? = Is it allowed to smoke here?
• Можно войти? = May I come in?
• После работы можно отдохнуть. = After work, one can rest.

In your sentence, можно sounds more like it’s okay / we’re free to rather than explicitly we are able to.

If you said мы можем лечь спать попозже, that would also work, but it sounds a bit more direct and personal: we can go to bed later.

Because лечь спать means to go to bed, while спать means to sleep.

So the sentence is about the act of going to bed later, not about sleeping later.

• лечь спать = to lie down to sleep / to go to bed
• спать = to sleep

Examples:

• Я лёг спать в полночь. = I went to bed at midnight.
• Я спал до десяти. = I slept until ten.

In your sentence:

• можно лечь спать попозже = we can go to bed a bit later

That is more precise than just можно спать попозже, which could suggest sleep later in a different sense.

Because лечь is the perfective verb, and here Russian is talking about a single completed action: going to bed later on this particular night.

• лечь = perfective
• ложиться = imperfective

Compare:

• Я обычно ложусь спать в одиннадцать. = I usually go to bed at eleven.
  
  • habitual, repeated action → imperfective
• Сегодня можно лечь спать попозже. = Today we can go to bed later.
  
  • one конкретный act → perfective

So лечь fits because the speaker means one specific bedtime event.

Попозже means a bit later / somewhat later.

• позже = later
• попозже = a little later

The prefix по- often softens or makes the meaning less absolute.

So:

• лечь спать позже = go to bed later
• лечь спать попозже = go to bed a bit later

In this sentence, попозже sounds natural and conversational, as if the speaker means not much later, just later than usual.

Because Раз завтра у нас выходной is a subordinate clause giving the reason, and it is separated by a comma from the main clause.

Structure:

• Раз завтра у нас выходной, = reason clause
• то можно лечь спать попозже. = main clause

Russian punctuation regularly uses commas to separate subordinate clauses like this.

It is neutral to somewhat conversational.

The main reason is раз in the sense of since. That usage is very common in speech and informal writing.

• Раз завтра у нас выходной, то можно лечь спать попозже.
  sounds natural in everyday conversation

A more formal or bookish version might use:

• Поскольку завтра у нас выходной, можно лечь спать попозже.
• Так как завтра у нас выходной, можно лечь спать попозже.

So the original sentence is perfectly normal, but not especially formal.

Yes. Russian word order is flexible, though some versions sound more natural than others.

Possible variants:

• Раз завтра у нас выходной, то можно лечь спать попозже.
• Раз у нас завтра выходной, то можно лечь спать попозже.
• Можно лечь спать попозже, раз завтра у нас выходной.

All of these are understandable and natural.

The original version sounds smooth because it puts the time word завтра early, which is often where speakers place important context.

Yes, that is an excellent natural translation.

A few good English versions are:

• Since we’re off tomorrow, we can go to bed later.
• Since tomorrow is our day off, we can go to bed a bit later.
• Because we have tomorrow off, we can stay up a little later.

The last version is slightly freer, because лечь спать попозже literally means go to bed later, not exactly stay up later, though in context the idea is basically the same.