Forbindelsen er mere stabil om morgenen end om aftenen.

Because Danish usually adds the definite article to the end of the noun.

• en forbindelse = a connection
• forbindelsen = the connection

The ending -en is the definite article for a singular common-gender noun. So the sentence is talking about the connection, not just a connection.

Adjectives in Danish often agree with the noun they describe, even after er.

Here, forbindelsen is:

• singular
• common gender

So the adjective stays in its basic form:

• forbindelsen er stabil
• forbindelsen er mere stabil

If the subject were a neuter noun, you would normally use -t:

• netværket er stabilt
• netværket er mere stabilt

In Danish, many adjectives—especially longer ones or words of foreign origin—form the comparative with mere rather than with an -ere ending.

So:

• stabil = stable
• mere stabil = more stable

For this adjective, mere stabil is the normal and natural choice.

Here om is used in time expressions and means something like in / during / in the mornings / in the evenings, depending on context.

So:

• om morgenen = in the morning / in the mornings
• om aftenen = in the evening / in the evenings

It is very common with parts of the day:

• om dagen = during the day
• om natten = at night
• om aftenen = in the evening

That is just the normal Danish pattern in these time expressions. After om, parts of the day are often expressed in the definite form:

• om morgenen
• om aftenen
• om natten

This does not necessarily feel as specifically definite as English the morning. It is more of a fixed idiomatic structure.

End is the Danish word used after a comparative, like English than.

So:

• mere stabil end ... = more stable than ...

Compare:

• større end = bigger than
• bedre end = better than

Yes, normally you do.

The natural structure is:

• om morgenen end om aftenen

That is because om belongs to each time expression. In English, you also repeat the preposition naturally: in the morning than in the evening.

Leaving out the second om would sound incomplete or unnatural.

In this sentence, it most naturally means a general pattern or usual tendency:

• the connection is more stable in the mornings than in the evenings

If you want to talk about a specific morning or evening, Danish usually uses different expressions, such as:

• i morges = this morning
• i aften = this evening
• i aftes = this evening / last night, depending on context

So this sentence sounds general, not tied to one specific day.

Yes. That is completely correct.

Danish main clauses follow the V2 rule, which means the finite verb usually stays in the second position. So if you move the time phrase to the front, the verb comes before the subject:

• Forbindelsen er mere stabil om morgenen end om aftenen.
• Om morgenen er forbindelsen mere stabil end om aftenen.

Both are correct. The second version puts slightly more focus on when this is true.

Not necessarily. Forbindelse can refer to different kinds of connections, depending on context, for example:

• an internet or phone connection
• a transport connection
• a link or connection between things

So the grammar of the sentence is general, even if the real-life context may make one meaning more likely.