Learn Dutch: We zitten al uren in het stoombad. - We have been sitting in the steam bath for hours.

To emphatically say "Boy, have we been sitting in the steam bath for hours!", you would start with Of, change the word order to make it a subordinate clause by moving the verb to the end, and say: Of we al uren in het stoombad zitten!

Why does the Dutch sentence use the present tense (zitten) when the English translation uses the present perfect continuous (have been sitting)?

In Dutch, when an action started in the past and is still ongoing in the present, you use the simple present tense along with a word indicating time duration. English requires the present perfect continuous for this, which makes it a very common trap for English speakers learning Dutch.

Could we use zijn (to be) instead of zitten (to sit) here?

You could grammatically say We zijn al uren in het stoombad, but Dutch strongly prefers using posture verbs like zitten, staan, or liggen to describe physical location. Since people typically sit in a steam bath, zitten sounds much more idiomatic to a native speaker.

What is the specific function of al before uren?

While al translates directly to "already," in continuous time expressions like al uren (for hours) or al jaren (for years) it acts as an emphasis marker. It highlights the length of the ongoing duration, reinforcing that you have been doing this continuously right up to the present moment.