how long does it take for dna to copy itself?

Answer 1

depends on the cell type.

Bacteria can do it relatively quickly because it has a tiny genome. Under ideal conditions they can do it in a few minutes.
Eukaryotic cells have genomes thousands of times bigger, yet because of the multiple replication forks, they can usually do it within a couple hours.

Answer 2

It depends on the kind of DNA, some bacterial DNA can replicate in a matter of minutes

Answer 3

it depends on the cell that is copying its DNA
heart cells make take months or years
skin cells take hours