How long should a meeting be?
Almost nobody chooses a meeting length. They accept the one the calendar offered, which is thirty or sixty minutes, and then fill it.
The one-hour default comes from calendar software
Calendar tools block time in half-hour increments because that is a convenient grid to draw, and the length you pick is almost always the first one offered. It is a UI decision that became a norm, with no research behind it.
You can see this in how meetings behave: work expands to fill whatever was booked. A decision that would have taken twelve minutes takes the full hour because the hour was there. Shortening the slot rarely loses anything, because the extra time was not doing work.
Match the length to the job
A status update needs fifteen minutes and usually did not need to be a meeting. A single decision with the right people in the room needs twenty to thirty. Working through a problem with real disagreement in it needs forty-five to sixty, and trying to do it in twenty produces a follow-up meeting.
Anything past ninety minutes is two meetings that have not been separated yet. Attention does not survive it, and the second half is usually spent re-litigating the first.
Find a time with a poll
Propose a few slots, share one link and let the group vote. Guests don't need an account.
Shorter meetings need more preparation, not less
The reason long meetings persist is that they absorb missing preparation. If nobody has read the document, the first twenty minutes become reading time, and the meeting has to be long enough to contain that.
So a twenty-five minute meeting is a commitment to send the context beforehand and to expect people to have looked at it. That is a real cost, borne by the organiser, and it is why the hour survives: it is cheaper for one person to book more time than to prepare.
End early on purpose
Booking twenty-five instead of thirty, or fifty instead of sixty, gives everyone a gap to move, write down what was decided, or take a break. Most calendar tools can make this the default so nobody has to argue for it each time.
It also contains overruns. With no gap, one meeting running five minutes late makes the next one late, and by mid-afternoon a single overrun has propagated through half a dozen people's days.
What to do when you cannot tell
If you do not know how long something needs, book the shorter option and say you will schedule a second session if it is not finished. People treat a meeting that might end early very differently from one that will certainly run to the hour.
The one thing worth avoiding is picking the length before knowing the purpose. If you cannot say in one sentence what the meeting decides, do not book it at all.