Learn Hardcore Finnish: Seuraava käynti kestää vain vartin, jos tulen ajoissa. - The next visit will last only a quarter of an hour if I arrive on time.

Finnish commonly uses the present tense for future meaning when the time is clear from context. Here, seuraava käynti (the next visit/appointment) makes it naturally future, so kestää can mean “will last,” and tulen can mean “if I (will) arrive.”

What exactly does käynti mean here? Is it “visit” or “appointment”?

Käynti literally means “a going/visit,” and in everyday Finnish it often refers to an appointment-type visit (e.g., a doctor’s visit, a quick stop somewhere). Depending on context, it can be translated as visit, appointment, or a (quick) stop.

Why is it seuraava käynti and not seuraavan käynnin?

Because seuraava käynti is the subject of the sentence: “The next visit lasts…”. Subjects are typically in the nominative case (basic dictionary form).

seuraava käynti = “the next visit” (subject)
seuraavan käynnin would be a form used when “the next visit” is an object (e.g., “I cancelled the next visit”).

What form is vartin, and why isn’t it varttia or vartti?

Vartin is the genitive singular of vartti (“quarter [of an hour]” → “15 minutes”). Finnish often uses:

genitive/accusative-like forms for a complete, exact duration: kestää vartin = “lasts (exactly) 15 minutes”
partitive for a more open-ended/ongoing/approximate duration: kestää varttia = “lasts for 15 minutes (roughly / at least / duration as an ongoing span)”

In practice, both can be heard, but vartin strongly suggests a neat, bounded “only 15 minutes.”

Does vain vartin mean “only for 15 minutes” or “only a quarter (of something)”?

Here it means only 15 minutes. Vartti in time expressions is a fixed, very common word meaning a quarter of an hour (15 minutes). So:

vain vartin = “only 15 minutes”

Why is vain placed before vartin? Could it go elsewhere?

Placing vain right before vartin clearly limits the duration: only 15 minutes. You could also move it for emphasis, but it may shift what “only” focuses on:

Seuraava käynti kestää vain vartin = only the duration is short (most natural)
Vain seuraava käynti kestää vartin = only the next visit lasts 15 minutes (contrast with other visits)
Seuraava käynti vain kestää vartin = can sound contrastive/colloquial, often implying “it just lasts 15 minutes (nothing more)”

What is the grammar of jos tulen ajoissa?

It’s a conditional clause:

jos = “if”
tulen = “I come / I arrive” (1st person singular of tulla)
ajoissa = “on time”

So jos tulen ajoissa = “if I arrive on time.”

What case or form is ajoissa? Why not something like ajassa?

Ajoissa is a fixed adverb meaning “on time.” Historically it’s based on the noun aika (“time”) in a plural inessive-type form (ajoissa), but you don’t need to actively “decline” it yourself in normal use—it’s learned as an adverb:

ajoissa = on time
myöhässä = late
Ajassa would mean something like “in the time / within the time” in other contexts, but it doesn’t function as the everyday “on time” adverb.

Can the sentence be reordered as Jos tulen ajoissa, seuraava käynti kestää vain vartin?

Yes. Both orders are correct:

Seuraava käynti kestää vain vartin, jos tulen ajoissa.
Jos tulen ajoissa, seuraava käynti kestää vain vartin.

Starting with the jos-clause often foregrounds the condition (“If I’m on time…”). Finnish word order is flexible, and commas help show the clause boundary.

Why is there a comma before jos?

Because jos tulen ajoissa is a dependent (subordinate) clause. Finnish normally uses a comma to separate a subordinate clause from the main clause, whether it comes at the end or the beginning.

Does kestää always take a time expression like this? What kind of “object” is vartin?

With kestää (“to last”), a duration often behaves like an object-like complement, and Finnish commonly uses:

partitive (especially if the duration is seen as unbounded/ongoing/approximate)
genitive/accusative-like forms (especially if the duration is exact/complete)

So vartin is functioning as a duration complement (object-like), expressing how long the visit lasts.

Could I say Seuraava käynti kestää vain 15 minuuttia instead?

Yes, that’s perfectly natural:

Seuraava käynti kestää vain 15 minuuttia, jos tulen ajoissa.

Using vartin is just a very common, concise way to say “15 minutes.”