The average duration for a single blink of a human eye is 0.1 to 0.4 seconds, or 100 to 400 milliseconds, according to the Harvard Database of Useful Biological Numbers. For purposes of comparison, the tick sound made by a clock lasts about one second. So it would be possible to blink three times during a single tick of a clock.
Blinking, Winking and Nods
Blink duration and blink rate -- the number of times a person blinks per minute -- are controlled by a central mechanism in the brain. This mechanism can be affected by medications, fatigue, disease, illness and even the age of an individual. As such, both blink duration and blink rate may slow down when a person is tired, sick or using sedative drugs. Alternatively, blink rate and blink duration may speed up when using stimulant drugs like caffeine. This means that the duration of a blink can vary, not only from one individual to another, but from blink to blink.