Is this question about drivers that turn off their indicators while still mid-turn? Or about drivers that turn or change lanes in very little time at all?

IMO, the correct time to use indicators is precisely when in preparation for a turning or lane-change manoeuvre, during such manoeuvre, and that’s it. Once the manoeuvre is done, the indicators should be extinguished to avoid ambiguity, unless a follow-up manoeuvre is planned.

I see no logical reason to enforce a prescribed minimum for indicator time, and it’s why I see minimum-three-blink on some modern cars as an anti-feature. After all, there’s no minimum (nor maximum) time to prepare and make a turning manoeuvre.

To use a USA example, the driving style of Los Angeles Intercity freeways is – for betre or worse – going to necessitate fairly quick lane changes, because of the tighter spacing between cars. In hard figures, a lane change might be prepped and done in 3 seconds. Some might say that all these drivers are violating good driving behaviors for following each other so closely, but it’s sadly a practical necessity when no amount of “just one more lane” can solve the systemic issues with regional road transportation there; it’s why LA is doubling down on public transit building.

Compare this with changing lanes on a rural Interstate freeway to pass a semi-truck, where a lane change can be more sedate because there might not be any other traffic in sight except for the two vehicles involved. Smooth driving on a road-trip might have this manoeuvre prepped and completed over 10-15 seconds, as the car might also be accelerating while also changing lanes.

In both circumstances, the indicators should remain blinking while mid-manoeuvre. Anything short of that is “too quick” in my book.

But if your question is how far in advance should drivers begin indicating before the manoeuvre, that’s a joint matter of regional convention and of law. And the former usually is the strongest influence.