Cells come in many sizes. They all aren't the same
Most cells are microscopic and can be seen only with microscopes. However, some nerve cells can be in excess of one meter long. The cells are adapted to carry information to and from all parts of the body. See the related link for a brief description of the cells and some diagrams.
On an adult human, yes.
depends, could be over a meter long, could be less than a millimetre, it all depends upon if you have a sensory/motoric neuron or a switching-neuron
A day
A pencil could be greater than 1 meter long, and it could be less than 1 meter long. But if it were greater than 1 meter, it would be impossible to write with, and I have never seen one that's longer than 1 meter.
about one meter for the human genome IIRC.
If you take all the DNA from a single human cell and stretch it into a single connected line, the DNA polymer will be about 1 meter long (1.02 m to be more accurate).
More than a half meter
90 to 120 days
The longest cells are neurons (nerve cells) with a length of 90cm-100cm linking the central nervous system (brain and spinal cord) to other parts of the body.
Meter rulers, a rope of length one meter? More generally things of a human scale are around a meter, desks tend to be about a meter and a half long, bookcases tend to be around a meter wide, doors are normally around a meter wide and so on. (plus or minus about half a meter!)