How much? How long?
It depends on the steroids
potency (they differ), the length of time you take it, and the amount you are taken.
Very modest suppression can occur within a week, because acth production by the pituitary will decrease, but reawaken in a couple of days. However high doses for along period (1mo) will atrophy the adrenal gland and you will need to taperm commencing with an alternate day regimen.