How long does it take to create metamorphic rock?

Question

Out of igneous and sedimentary?

Answer 1

It really depends on how much pressure/heat is being put on the rock. If is possible to change a regular igneous/sedimentary rock into its metamorphic counterpart in a matter of seconds if you apply enough stress. More often than not the process is very slow and will take hundreds if not thousands of years.

Answer 2

It depends. Certain minerals will Lithify at different temps. Each one has to reach a certain amount of pressure to metamorphose. Quartz for example does not take much pressure to change form.