Vi måste kontrollera öppettiden på hemsidan först.

Because after the modal verb måste (must / have to), Swedish normally uses the infinitive without att.

• vi måste kontrollera = we must check
• vi vill kontrollera = we want to check
• vi kan kontrollera = we can check

This is similar to English, where you say must check, not must to check.

No—this is a very common false friend.

In this sentence, kontrollera means:

• check
• verify
• make sure of

So kontrollera öppettiden means check the opening time / opening hours.

If you want control in the sense of manage or be in charge of, Swedish often uses words like:

• styra = control/govern
• ha kontroll över = have control over

So here, kontrollera is much closer to check than to English control.

Swedish often forms compound nouns by joining words together.

Here:

• öppet = open
• tid = time

Together, öppettid means opening time or can refer to opening-hours information depending on context.

Then the definite ending is added:

• öppettid = opening time
• öppettiden = the opening time

So Swedish writes this as one word, not as separate words.

Both can be possible, but they are slightly different.

• öppettiden = the opening time / the relevant opening-hours info
• öppettiderna = the opening hours (plural), often the full schedule

A learner may expect the plural because English often says opening hours. Swedish can also say that:

• Vi måste kontrollera öppettiderna på hemsidan först.

That is very natural if you mean the full set of hours.

The singular öppettiden can sound like you are checking the specific time the place opens, or the opening-time information as a single item.

Because Swedish usually puts the definite article at the end of the noun instead of using a separate word like English the.

• hemsida = homepage / website
• hemsidan = the homepage / the website

The same happens with öppettiden:

• öppettid = opening time
• öppettiden = the opening time

So the -n ending here is doing the job that the does in English.

Swedish normally uses på for websites and pages:

• på hemsidan = on the website
• på internet = on the internet

This matches English quite closely: we also usually say on the website.

Using i would sound strange here, because i usually means in in a more physical or enclosed sense.

In everyday Swedish, hemsida is often used loosely to mean website, even though literally it originally means homepage.

Useful distinctions:

• hemsida = often used in everyday speech for website
• webbplats = website, more precise/formal
• webbsida = webpage
• startsida = homepage/start page

So in normal conversation, på hemsidan often just means on the website.

Because that is a very natural place for it in Swedish when it means first / before doing anything else.

The basic structure here is:

• Vi = subject
• måste = finite verb
• kontrollera öppettiden = infinitive phrase + object
• på hemsidan = place
• först = adverb

Putting först at the end gives the sense:

We need to check the opening time on the website first.

If you move först, the emphasis changes a bit:

• Först måste vi kontrollera öppettiden på hemsidan.
  = First of all, we need to check the opening time on the website.

So the final position is natural when first modifies the whole action.

The word order is very standard Swedish main-clause order:

Vi måste kontrollera öppettiden på hemsidan först.

Breakdown:

1. Vi = subject
2. måste = finite verb in second position
3. kontrollera = infinitive
4. öppettiden = object
5. på hemsidan = adverbial phrase
6. först = adverb

A useful thing to notice is that Swedish main clauses usually keep the finite verb early in the sentence. Here, måste comes right after the subject.

A rough pronunciation guide:

• måste ≈ MOS-teh
  The å sounds somewhat like the vowel in British more, but shorter.

• öppettiden ≈ UP-eh-tee-den
  The ö sound does not exist exactly in English. It is somewhat like the vowel in British bird or burn, but with rounded lips.

A few important sound points:

• ö is not the same as o
• double consonants usually make the preceding vowel short
• stress is mainly near the beginning of the word

If you are learning pronunciation, ö and å are worth practising separately, since they change meaning.

Sometimes, but not always.

• vi måste kontrollera = we must / have to check
• vi behöver kontrollera = we need to check

Both can work, but måste is usually stronger and more necessary. Behöver can sound a little softer or more like a practical need.

So:

• Vi måste kontrollera öppettiden på hemsidan först.
  = We really have to do that first.

• Vi behöver kontrollera öppettiden på hemsidan först.
  = We need to check it first.

Both are natural, but måste gives a stronger sense of obligation or necessity.