Místo abychom větrali celý den, větráme krátce.

It means instead of us ... / rather than ....

A fuller version would be místo toho, abychom..., literally instead of that, that we..., but Czech often leaves out toho when the meaning is clear.

So:

• Místo abychom větrali celý den... = Instead of airing/ventilating all day...

This is a very common Czech way to express instead of doing X, we do Y.

Abychom is the we form of aby.

The word aby often introduces a clause meaning something like:

• so that
• in order that
• for someone to

With person endings, you get forms like:

• abych = so that I
• abys = so that you
• aby = so that he/she/it/they
• abychom = so that we
• abyste = so that you (plural/formal)

In this sentence, abychom is part of the construction místo abychom... = instead of us...

Good question. After abychom, Czech uses a form that looks like the past tense, but here it is not actually past tense.

So:

• větrali jsme = we aired / we were airing in the past
• abychom větrali = for us to air / if we were to air / instead of airing

The form větrali here is part of the aby construction, not a normal past-tense statement.

So even though it looks past, the meaning is not we aired. In this sentence it just belongs to the structure místo abychom větrali...

Yes, větraly is possible in the right context.

In Czech, this type of verb form agrees with the gender of the plural subject:

• větrali = mixed group or a group including at least one male
• větraly = all-female group

So the sentence as written assumes a general/mixed we, or at least one male in the group.

If a group of women were speaking, they could say:

• Místo abychom větraly celý den, větráme krátce.

Notice that the second verb větráme does not show gender, so only the větrali / větraly part changes.

Větrat means to air out or to ventilate.

In everyday Czech, it often means opening a window to let fresh air into a room:

• větrat pokoj = to air out a room
• větrat byt = to air out an apartment

So in this sentence, the idea is probably airing the room/house rather than technical ventilation.

Větráme is the 1st person plural present tense of větrat:

• já větrám = I air out
• my větráme = we air out

Here it expresses a general habit, method, or recommendation, not necessarily something happening at this exact moment.

So the sentence has the sense of:

• Rather than airing all day, we air briefly
• or Instead of keeping the windows open all day, we ventilate for a short time

Because krátce is an adverb, and it modifies the verb větráme.

• krátký = short, an adjective
• krátce = briefly / for a short time, an adverb

Here we are describing how we air out the room, so Czech needs the adverb:

• větráme krátce = we air out briefly

You could also hear similar alternatives such as:

• větráme jen krátce = we air out only briefly
• větráme na krátkou dobu = we air out for a short time

But krátce is compact and natural.

Because Czech often uses the accusative to express duration of time.

So:

• celý den = all day / for the whole day
• celou noc = all night
• celý týden = all week
• dvě hodiny = for two hours

That is why Czech does not need a preposition like English for here.

Because the first part is a subordinate clause:

• Místo abychom větrali celý den = subordinate clause
• větráme krátce = main clause

Czech normally separates these with a comma.

So:

• Místo abychom větrali celý den, větráme krátce.

But there is no comma between místo and abychom.

Yes. That is a perfectly natural and slightly fuller version.

Compare:

• Místo abychom větrali celý den, větráme krátce.
• Místo toho, abychom větrali celý den, větráme krátce.

Both are correct. The second one sounds a bit more explicit because of toho, but the meaning is the same.

Because Czech normally does not use a bare infinitive after místo in this meaning.

Instead, Czech usually chooses one of these patterns:

• místo toho, abychom větrali...
• místo abychom větrali...
• místo celodenního větrání...

So English instead of airing all day often becomes either:

• a clause with aby
• or a noun phrase

A bare infinitive after místo would sound non-standard or unnatural here.

The sentence uses the imperfective větrat because it talks about the manner and duration of the action in a general way:

• větrat celý den
• větrat krátce

That fits imperfective aspect very well.

The perfective verb vyvětrat means something more like to air out completely / to finish airing out.

So:

• větráme krátce = we air out briefly, as a general method
• vyvětráme = we air it out and complete the action

In some contexts, vyvětrat could also be possible, but this sentence is naturally phrased with větrat because it focuses on how long the airing lasts, not on the completed result.