Jeśli skończymy projekt przed terminem, szefowa da nam premię zamiast kolejnych nadgodzin.

In Polish, after jeśli (if), you normally do not use a special future tense the way English does. Instead, Polish often uses a present-form verb with future meaning, especially when the verb is perfective.

• skończymy = grammatically a present-form verb
• but because skończyć is perfective, it refers to a completed future action
• so jeśli skończymy projekt means if we finish the project

This is very natural in Polish:

• Jeśli przyjdziesz, porozmawiamy. = If you come, we’ll talk.
• Jeśli zdążę, zadzwonię. = If I make it in time, I’ll call.

This is a question of aspect, which is very important in Polish.

• skończyć = perfective → to finish, to bring something to completion
• kończyć = imperfective → to be finishing, to finish in a general/repeated/process sense

In this sentence, the idea is completing the project before the deadline, so skończyć is the right choice.

Compare:

• Jeśli skończymy projekt... = If we finish the project...
  (a completed result)
• Jeśli kończymy projekt... = this sounds odd here, and would suggest an ongoing or habitual idea rather than a one-time completed result

Because przed usually requires the instrumental case when it means before in the sense of time or position.

So:

• termin = nominative
• terminem = instrumental

That is why:

• przed terminem = before the deadline

This is a common pattern:

• przed obiadem = before lunch
• przed spotkaniem = before the meeting
• przed domem = in front of the house

Szefowa means female boss / woman boss, while szef means male boss (and sometimes informally can refer to a boss in general, depending on context).

So the sentence tells you that the boss is a woman:

• szefowa da nam premię = the female boss will give us a bonus

This is just lexical meaning, not a grammar rule specific to this sentence.

Da is the future form of dać (to give, perfective). Since the sentence refers to a single completed future action, the perfective verb is the natural choice.

• da = will give
• będzie dawać would mean something more like will be giving or repeated/ongoing giving, which does not fit as well here

So:

• szefowa da nam premię = the boss will give us a bonus

Because dać is perfective, its present-form conjugation is used with future meaning:

• dam, dasz, da, damy, dacie, dadzą

Because dać komuś coś means to give someone something.

Polish uses the dative case for the person receiving the thing.

Here:

• my = we
• nam = to us

So:

• szefowa da nam premię literally = the boss will give to us a bonus

Other examples:

• Da mi książkę. = She’ll give me the book.
• Damy wam znać. = We’ll let you know. / We’ll give you notice.

Because premia is the direct object of dać, so it goes into the accusative case.

• nominative: premia
• accusative: premię

So:

• da premię = will give a bonus

This is a regular pattern with many feminine nouns ending in -a:

• kawa → kawę
• nagroda → nagrodę
• premia → premię

After zamiast (instead of), Polish uses the genitive case.

That is why you get:

• kolejne nadgodziny = nominative / accusative plural
• kolejnych nadgodzin = genitive plural

So:

• zamiast kolejnych nadgodzin = instead of more/additional overtime

This is a very useful pattern:

• zamiast kawy = instead of coffee
• zamiast obiadu = instead of lunch
• zamiast prezentów = instead of gifts

Because kolejnych means further, additional, more, subsequent, and it agrees with nadgodzin in case, number, and gender.

Base forms:

• kolejne nadgodziny = additional overtime hours After zamiast:
• zamiast kolejnych nadgodzin

So the sentence means the boss will give a bonus instead of making us do more overtime.

Also note:

• nadgodziny is a plural noun meaning overtime
• in the genitive plural, it becomes nadgodzin

Yes. Polish usually treats nadgodziny as a plural noun.

So you commonly see forms like:

• pracować w nadgodzinach = to work overtime
• mieć nadgodziny = to have overtime hours
• uniknąć nadgodzin = to avoid overtime

English overtime is often uncountable, but Polish nadgodziny behaves more like overtime hours.

Yes, Polish word order is more flexible than English, because cases show the grammatical roles. The sentence as given is neutral and natural:

• Jeśli skończymy projekt przed terminem, szefowa da nam premię zamiast kolejnych nadgodzin.

You could rearrange parts for emphasis, for example:

• Szefowa da nam premię, jeśli skończymy projekt przed terminem.
• Jeśli przed terminem skończymy projekt, szefowa da nam premię.

These all mean basically the same thing, but the emphasis shifts slightly:

• putting jeśli... first sets up the condition first
• putting szefowa da nam premię first highlights the result first

Yes. In Polish, when a subordinate clause with jeśli comes first, it is normally separated from the main clause with a comma.

So:

• Jeśli skończymy projekt przed terminem, szefowa da nam premię...

This is standard Polish punctuation.

You can also have the main clause first:

• Szefowa da nam premię, jeśli skończymy projekt przed terminem.

There is still a comma before jeśli because it introduces a subordinate clause.

Not usually in this context. Premia most naturally means:

• bonus
• sometimes bonus payment
• sometimes performance bonus

In a workplace sentence like this, bonus is definitely the best translation.

• nagroda would be more like prize or award
• premia fits salary/workplace language much better

So:

• szefowa da nam premię = the boss will give us a bonus