A delayed connection pushed me one day past my visa's validity — how much trouble is a one-day overstay?

Speaking generally rather than about your specific case, since the rules and their application differ by country and only the relevant authority can tell you where you stand.

The pattern people report is that a short overstay with a documented, involuntary cause is usually treated as an administrative matter rather than a serious one. The two things that consistently make the difference:

• Documentation. Keep everything the airline gave you — the rebooking, the hotel voucher, the delay notice, the original ticket showing the intended departure date. This is the entire evidentiary basis for "involuntary", and it is far easier to keep it than to obtain it later.
• Disclosure. Raising it yourself at departure control is generally better received than having it discovered. It is going to be seen either way, because exit is where the dates get compared.

Expect it to be recorded in some form even if nothing further happens. A recorded, explained overstay is a very different thing from an unexplained one on a future application.

From the airport side: the officer at exit control is not usually the person who decides anything. They are the person who notices, documents and refers.

So what you can control is how complete the record is when it leaves their hands. Have the airline documents out and in order before you reach the desk, be able to state the sequence in two sentences, and do not editorialise about whose fault it was.

If you are asked to give a written statement, that is a normal part of the process rather than a sign that something has escalated. Write what happened, attach the airline paperwork, keep a copy of everything including anything you sign.

And keep a copy of the exit stamp or the record of departure. If a question ever comes up years later on a visa application, evidence of when you actually left is the thing you will wish you had.

The forward-looking lesson, which is the genuinely useful part for everyone reading: never plan to use the last day of a visa.

This is the standard advice among people who travel on visas regularly, and this thread is exactly why. A visa's final day is not a target, it is a hard edge, and any of a dozen ordinary travel failures — a delay, a cancellation, a strike, weather, illness — can push you across it with no decision on your part.

Building in two or three days of margin costs nothing when the trip goes normally and removes the entire category of problem when it does not. It is the cheapest insurance in travel planning.

One practical addition for the moment it happens rather than afterwards: when the airline rebooks you onto a flight that lands you outside your permitted dates, say so at the rebooking desk.

Sometimes there is an earlier option that they did not offer because they were optimising for seats rather than for your dates. And if there genuinely is not one, you have created a contemporaneous record that you raised it, which is worth more than reconstructing the story later.