YouTube’s own creator guidance says there is no universal ideal length. A joke can be twenty seconds. A careful tutorial can be twenty minutes. Stretching either one to fit a rumor about “the algorithm” usually adds filler that people skip.
What the systems do notice is whether viewers stay and whether they look satisfied afterward. Watch time and retention curves are more honest than a target number. If people leave at minute three, the problem is often the third minute—not the fact that the video is twelve minutes long.
Shorts and long videos are different rooms. A vertical clip can introduce an idea; a longer video can finish it. One format winning with one audience does not prove the other format is dead.
After you publish, the useful homework is the graph. Look for the drop, ask what promised more than it delivered, and edit the next opening. Evidence beats a thread that claims every hit must be eight minutes and seventeen seconds.
Respect the viewer’s clock. If you can show the result sooner, do. If the craft needs patience, say so in the title so the right people sit down.