Åbningstiden på lørdag passer mig ikke, så jeg kommer hellere på mandag.

Åbningstid means opening time/opening hours in a general sense.

Åbningstiden has the definite ending -en, so it means the opening time / the opening hours.

Danish often uses the singular form where English prefers a plural:

• åbningstid = opening hours
• lukketid = closing time / closing hours

So åbningstiden på lørdag means the Saturday opening hours or the opening time on Saturday.

Yes. Danish very often joins nouns into one word.

Here:

• åbning = opening
• tid = time

Together:

• åbningstid = opening time / opening hours

Then the definite article is added to the end:

• åbningstid → åbningstiden = the opening time/hours

This is very common in Danish:

• arbejdstid = working hours
• fritid = free time
• ankomsttid = arrival time

Yes. In this sentence, på corresponds to English on with days.

So:

• på lørdag = on Saturday
• på mandag = on Monday

This is a very common way to talk about specific upcoming days.

Be careful not to confuse it with:

• om lørdagen = on Saturdays / on Saturday generally
• i lørdags = last Saturday

Usually it means the Saturday that is coming next from the speaker’s point of view.

So if today is Wednesday, på lørdag normally means the upcoming Saturday.

Likewise:

• på mandag usually means the coming Monday

In real life, context decides everything, and speakers may clarify if needed.

Here passe means to suit, to be convenient for, or to work for someone.

So:

• Det passer mig = That suits me / That works for me
• Det passer mig ikke = That doesn’t suit me / That doesn’t work for me

In your sentence, the subject is åbningstiden på lørdag:

• Åbningstiden på lørdag passer mig ikke
  = The opening hours on Saturday don’t suit me

This use of passe is very common in Danish.

Because mig is the object form of jeg.

Compare:

• jeg = I
• mig = me

In this sentence, åbningstiden på lørdag is the thing doing the action grammatically, and mig is the person affected by it:

• Åbningstiden ... passer mig ikke

That is like English:

• The time doesn’t suit me not
• The time doesn’t suit I

So Danish uses mig, just as English uses me.

Because in this kind of main clause, ikke usually comes after the object or complement.

So Danish naturally says:

• Det passer mig ikke
• Han kender mig ikke
• Jeg kan lide det ikke is not normal Danish

In your sentence:

• passer = verb
• mig = object
• ikke = negation

So passer mig ikke is the normal word order.

Så here means so, therefore, or as a result.

It links the two ideas:

• The opening hours on Saturday don’t suit me
• so I’d rather come on Monday

So it shows consequence: A doesn’t work, so B will happen instead.

Because hellere means rather, while bedre means better.

In this sentence, the speaker is choosing one option over another:

• Saturday does not work
• Monday is preferred instead

So Danish uses hellere:

• Jeg kommer hellere på mandag = I’d rather come on Monday

Compare:

• hellere = rather
• bedre = better

Examples:

• Jeg vil hellere blive hjemme. = I’d rather stay home.
• Mandag er bedre for mig. = Monday is better for me.

Both can sometimes be possible in similar situations, but they do not mean exactly the same thing.

Because Danish often uses the present tense for planned or arranged future actions, just like English sometimes does.

So:

• Jeg kommer på mandag literally looks like I come on Monday
• but it means I’m coming on Monday or I’ll come on Monday

This is completely normal Danish.

Other examples:

• Vi ses i morgen. = We’ll see each other tomorrow.
• Jeg rejser på fredag. = I’m leaving on Friday.

Yes, you could.

There is a small difference in feel:

• jeg kommer hellere på mandag sounds natural and direct
• jeg vil hellere komme på mandag sounds a bit more explicit: I would rather come on Monday

The original version is very idiomatic in everyday Danish.

It can mean both, depending on context.

In a sentence like this, komme often means:

• come by
• show up
• visit
• attend at that time instead

So jeg kommer hellere på mandag is not only about movement toward the speaker. It can simply mean: I’ll come in on Monday instead or I’ll show up on Monday instead.

A fairly literal version would be:

The opening hours on Saturday don’t suit me, so I’d rather come on Monday.

A few points are slightly less literal:

• åbningstiden is singular in Danish, though English often says opening hours
• kommer is present tense in Danish, but English often uses I’ll come or I’m coming
• hellere is literally rather

So the structure is very Danish, even if the meaning is straightforward.