no, it is not true. as soon as you take a steroid, and that steroid enters your blood stream, it is active and working.
this goes for all non esterfied steroids.
a steroid with an ester attached is inactive until enzymes in the blood remove the ester, and then the steroids becomes active and can bind to the androgen receptor.
but you take dianabol, and the next time you go piss, you will have dianabol metabolites in your urine.