In the UK the highway code is quite clear as to the use and minimum duration of signals.
Rule 103: Drivers and riders should make proper Highway Code signals to warn nearby traffic that you are intending to change course or direction. This includes providing directional information of your intended motions to other road users and pedestrians. Motorists should always:

    Give clear signals and use direction indicators in plenty of time.
    Check it is not misleading to signal at the time.
    Use signals to advise other road users before changing course, direction, stopping or moving off.
    Cancel the signalling devices after use.
    Apart from using direction indicators, there are other ways you can give signals. Use an arm signal to other road users to emphasize or reinforce the signalling from the vehicle if necessary.

and
Lane discipline
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If you need to change lane, first use your mirrors and if necessary take a quick sideways glance to make sure you will not force another road user to change course or speed. When it is safe to do so, signal to indicate your intentions to other road users and when clear, move over.