Any question about " duration of any drug or mineral or any other substance " to be calculated accurately: you need to do a plan of experimental work including the following:
1- Definition of "potassium dichromate" as regards is it : a drug used in a certain disease, dose or concentration, its route of administration, its metabolic pathway and before all in what species you will study this duration " in days" as rodents are different from human being and so on...
2- you have " potassium dichromate" already prepared or you will prepare it and in what dosage form will be, your question needs more clarification, is it related to pharmacology or other branches in medical science, please search in related researches : its half-life, its bioavailability, the transit time required to pass from GIT to blood if administered orally and other important pharmacokinetic properties.
3- The above points will help you to perform a " kinetic study" from zero time of administration till the end of therapeutic effect of your substance . if related to therapy, you can draw " area under the curve AUC" in a bioavailabilty lab. and you need the consultation of a professional experts in both pharmaceutics and pharmacokinetics
4- Either radioimmunoassay or histopathological studies on adrenal gland tissues" cortex and medulla" would help you hand-in-hand with the above scientific steps. Also ask the guidance of a histopathology expert
I answered you on the basis that you do a research on a therapeutic substance on adrenal gland, if you are working in another direction, my answer would be not beneficial to your goal. Your question is somewhat vague to me.