It means: not the last one, but the one before the last one.
A single word with the same meaning is penultimate.
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If you mean milliseconds, there are 1000 in a second
0.001 or 1/1000 of a second
I think you mean a nanosecond. This is 10-9 of a second
Rate at which the speed of the object is changing that is the acceleration.
If you mean the time measurement, the first. If you mean extremely small, the second.