Was de catering maar op tijd.

No. Even though it starts with the verb was, this is not a normal yes/no question.

Here, Dutch is using a wish construction:

• Was ... maar ...

This means something like if only ... were ... or I wish ... were ....

A real question would be:

• Was de catering op tijd? = Was the catering on time?

The word maar is one of the clues that this is a wish, not a question.

Because Dutch can put the verb first to express a wish.

So:

• Was de catering maar op tijd.

has the pattern:

• verb + subject + maar + rest

That is a fixed and common way to say if only...

You will see the same pattern in sentences like:

• Was ik maar rijk. = If only I were rich.
• Had hij maar geluisterd. = If only he had listened.

So the verb-first order here is grammatical and meaningful; it is not random inversion.

No. In this sentence, maar does not mean but.

Here maar is a modal particle that helps create the sense of a wish, regret, or longing. It adds the feeling of:

• if only
• I wish
• would that

So in this construction, you usually should not translate maar literally as but.

This is very common in Dutch: words like maar, toch, eens, nou often have special functions that are hard to translate word-for-word.

Dutch often uses a past tense form to express an unreal, unlikely, or wistful wish about the present.

So was here does not mainly point to past time. Instead, it gives the sentence a more hypothetical or regretful tone.

This is similar to English:

• If only the catering were on time
• I wish the catering were on time

So was is functioning a bit like English were in formal wish-statements.

In modern Dutch, this is a normal and very common pattern. It is not really about the catering being on time in the past.

It is a complete sentence.

To an English speaker, it may feel incomplete because English often uses a structure like:

• If only the catering were on time

which looks like part of a larger sentence.

But in Dutch, Was ... maar ... can stand by itself as a full exclamative sentence expressing a wish or complaint.

So nothing is missing grammatically.

Because catering is a de-word in Dutch.

Like many borrowed nouns, its gender has to be learned as part of the word:

• de catering

There is not always a simple rule that lets you predict whether a borrowed noun takes de or het, so it is best to memorize the article together with the noun.

In Dutch, de catering usually refers to:

• the catering service
• the food-and-drink provision
• the catering company or setup for an event

Op tijd means on time or in time, depending on context.

In this sentence it means that the catering is there, ready, or arrives when it should.

This is a very common Dutch expression:

• op tijd komen = to arrive on time
• op tijd zijn = to be on time
• op tijd klaar zijn = to be ready on time

So op tijd is a fixed phrase you should learn as a unit.

Yes. It is a borrowing from English, but it is fully used in Dutch.

That does not mean it works exactly like English in every situation. In Dutch, catering often refers specifically to:

• the catering service for an event
• the food service itself
• the company handling food and drinks

So even though the word looks familiar to an English speaker, it is still best to learn how Dutch speakers actually use it in context.

They are similar, but not identical in tone.

• Was de catering maar op tijd.
  This sounds like a stronger wish, often with frustration or regret. It can suggest that the speaker feels the situation is bad or unlikely.

• Als de catering maar op tijd is.
  This usually means something like as long as the catering is on time or I just hope the catering is on time. It is often more practical and less wistful.

So Was ... maar ... is the more emotional wish-pattern.

Very often, a sentence like this is written with an exclamation mark:

• Was de catering maar op tijd!

That matches the emotional tone of a wish or complaint.

A period is also possible, especially in quieter writing or dialogue, but the sentence itself still has an exclamative meaning.