Learn Hardcore German: Innerhalb von zwei Tagen klären wir die offenen Fragen, außerhalb dieser Zeit sind wir kaum erreichbar. - Within two days we clarify the open questions; outside this time we are hardly reachable.

Both innerhalb and außerhalb govern the genitive in standard German. In the first clause, Innerhalb von zwei Tagen uses the very common pattern innerhalb von + dative to avoid the rare genitive of a bare numeral (the formal genitive would be innerhalb zweier Tage). In the second clause, außerhalb dieser Zeit uses the straightforward genitive with a determiner: dieser is the genitive singular of diese. Using außerhalb von dieser Zeit is not standard; prefer außerhalb dieser Zeit. With place names or bare nouns, außerhalb von is common, e.g. außerhalb von Berlin.

Why is it zwei Tagen and not zwei Tage?

Because von takes the dative, so you need the dative plural: von zwei Tagen. Without von, the genitive after innerhalb would be innerhalb zweier Tage (formal) or, if the two days are specific/previously known, innerhalb der zwei Tage.

Can I say in zwei Tagen instead of innerhalb von zwei Tagen?

They mean different things:

in zwei Tagen = at a point in time two days from now.
innerhalb von zwei Tagen = within a time window of two days (by/within two days). Colloquial equivalents for “within” include in den nächsten zwei Tagen or binnen zwei Tagen.

What’s the difference between innerhalb, binnen, and während?

innerhalb (von) zwei Tagen = within two days (deadline/limit).
binnen zwei Tagen = within two days (slightly formal but common).
während der zwei Tage = during the two days (describes what happens in that period, not a deadline).

What exactly does kaum erreichbar mean?

It means “hardly reachable/scarcely contactable,” not “not reachable at all.” It implies you might reach us only rarely or with difficulty. Near-synonyms: nur schwer erreichbar, schlecht erreichbar, selten erreichbar (the last focuses on infrequency).

Does erreichbar refer to being contactable or physically reachable?

For people, erreichbar usually means “contactable/available” (by phone/email/chat). For places, it can mean “easy/hard to get to” (e.g., gut/schlecht erreichbar), but in your sentence it clearly means contactable.

Why is the verb before the subject: klären wir / sind wir?

German main clauses are verb‑second. If you front a time/place phrase (Innerhalb von zwei Tagen, Außerhalb dieser Zeit), the finite verb moves into second position and the subject follows: klären wir, sind wir. Neutral order is also possible: Wir klären die offenen Fragen innerhalb von zwei Tagen. Wir sind außerhalb dieser Zeit kaum erreichbar.

Why is there a comma between the two parts? Could I use a conjunction instead?

These are two independent main clauses. German requires a comma between asyndetically coordinated main clauses; a semicolon or a period would also be fine. You can add a conjunction for clarity/contrast, e.g. …, aber außerhalb dieser Zeit sind wir kaum erreichbar. Alternatives: jedoch, ansonsten/sonst.

Why is it die offenen Fragen (with -en) and not die offene Fragen?

With a definite article in the plural (die), adjectives take -en in all cases. Here, die offenen Fragen is accusative plural as the direct object of klären. Without the article, you’d say wir klären offene Fragen.

Does offene Fragen just mean “unanswered questions”?

Yes—offen here means “unresolved.” It’s a set phrase in business contexts: offene Fragen or offene Punkte (“open items”). It does not mean “frank/open-minded.”

What’s the difference between Fragen klären, Fragen beantworten, and erklären?

Fragen klären: to clarify/resolve issues (reach a decision or clarity).
Fragen beantworten: to answer questions (provide answers).
erklären: to explain something to someone (etwas jemandem erklären). Your sentence promises resolution, so klären is the best choice.

Can I say innerhalb zweier Tage instead of innerhalb von zwei Tagen?

Yes. innerhalb zweier Tage is grammatically correct and more formal/literary. In everyday use, innerhalb von zwei Tagen is more idiomatic.

Why außerhalb dieser Zeit and not außerhalb von dieser Zeit?

With außerhalb plus a determiner/pronoun, standard German uses the genitive: außerhalb dieser Zeit. außerhalb von is common with proper names or bare nouns (außerhalb von Berlin), but außerhalb von dieser Zeit is considered nonstandard.

What does dieser Zeit refer to?

It points back to the previously mentioned two‑day window. You could make that explicit by using a clearer noun: außerhalb dieses Zeitraums. Using Zeit is idiomatic shorthand for “that period.”

Can I use the future tense with werden here?

Yes: Innerhalb von zwei Tagen werden wir die offenen Fragen klären … This is more explicit about the future. The present tense with a time adverbial (klären wir) is also very common for planned future actions.

Could I use außer instead of außerhalb?

Not here. außer means “except for,” which excludes items, not “outside of” a time span. außer dieser Zeit would mean “except for this time,” which is a different meaning. You need außerhalb dieser Zeit for “outside that period.”