Nie zapomnijcie pójść do toalety przed długą podróżą, bo później nie będzie czasu.

Zapomnijcie is the imperative form of zapomnieć, and it is 2nd person plural. It means you are telling more than one person: don’t forget.

Related forms:

• nie zapomnij — said to one person, informal
• nie zapomnijcie — said to more than one person, informal

If you wanted to be more formal, Polish often uses a different structure, for example proszę nie zapomnieć.

After zapomnieć when you mean forget to do something, Polish normally uses an infinitive.

So:

• zapomnieć pójść
• zapomnieć zadzwonić
• zapomnieć kupić

This works like English forget to go / forget to call / forget to buy, but Polish does it with the plain infinitive form.

Because pójść is the perfective verb, and iść is imperfective.

In this sentence, the speaker means make that one trip to the toilet before the journey. That is a single completed action, so pójść fits better.

Very roughly:

• iść — to be going, to go in an ongoing sense
• pójść — to go once, to set off, to complete that trip

So nie zapomnijcie pójść do toalety sounds natural here.
Using iść would sound less natural in this context.

Do usually takes the genitive case when it means to or into with movement.

The noun is:

• toaleta — nominative

Its genitive singular form is:

• toalety

So:

• pójść do toalety = go to the toilet / restroom

This is a very common pattern in Polish:

• do domu
• do sklepu
• do szkoły
• do toalety

Because the preposition przed here means before, and in this meaning it takes the instrumental case.

The base form is:

• długa podróż — a long journey

In the instrumental singular, that becomes:

• długą podróżą

Both words change because the adjective must agree with the noun in:

• gender
• number
• case

So:

• podróż → podróżą
• długa → długą

Bo means because.

It is very common and natural in everyday Polish.
Yes, you could also use ponieważ, but ponieważ sounds a bit more formal or written.

So:

• bo później nie będzie czasu — very natural, conversational
• ponieważ później nie będzie czasu — also correct, but more formal

Because after negation, Polish often uses the genitive in expressions like there is / there will be.

Compare:

• będzie czas — there will be time
• nie będzie czasu — there won’t be time

So:

• czas is nominative
• czasu is genitive

This is a very common pattern:

• jest kawa / nie ma kawy
• będzie czas / nie będzie czasu

Yes, in a way.

English often needs a dummy subject: there won’t be time.
Polish does not need that extra word.

So nie będzie czasu is literally something like will not be time, but the natural English meaning is there won’t be time.

This kind of subjectless sentence is completely normal in Polish.

Yes. Polish word order is more flexible than English word order.

The given sentence is natural and neutral:

• Nie zapomnijcie pójść do toalety przed długą podróżą, bo później nie będzie czasu.

You can move things around for emphasis, but not every version sounds equally natural. The original is a normal way to give an instruction first and then give the reason.

For example, you could also say:

• Bo później nie będzie czasu, nie zapomnijcie pójść do toalety przed długą podróżą.

That is grammatical, but it puts more emphasis on the reason.

Do toalety is completely natural here.

It clearly means to the toilet / restroom.
In some contexts, Polish speakers also say do łazienki, especially when using bathroom as a polite or indirect way of referring to the toilet.

So both can occur, but:

• do toalety is direct and clear
• do łazienki can be slightly more euphemistic, depending on context

In this sentence, do toalety works very well.

Because in standard Polish punctuation, you normally put a comma before bo when it introduces the reason.

So:

• ..., bo później nie będzie czasu.

This is standard and expected in writing.

It can mean both, depending on context.

Here później means something like:

• later
• afterwards

So bo później nie będzie czasu means that at a later point, time will no longer be available. In this sentence, later is the most natural English match.