This is a misconception as to the morive for burning a suspevted witch at the stake or putting them on the ducking stool. the purpose wasn't to kill them, it was to prove whether they were really a witch, if they survived they were deemed a witch, if they drowned or were burnt they were innocent. Work that one out!
Can't swear to medieval times, but this was going on sometime in the 1600's. I'm not a historian, I just remember watching stuff like witchfinder general.
most trials took place between 1300 - 1500. but the grand book - the Malleus Malificarum - was written by two monks in 1428 (Sprenger and Kramer, Dominicans). It detailed the tortures to be used.
I don't think witches were ever burned in England; they were hanged. (They were burned on the continent.) As dot says, 'drowning' was more a test than a punishment.
Technically it spanned sub-medieval periods. The period in Brutain was (and still is) Post-medieval since the medieval period spanned between post-Roman (1st Century) and ended in around 1485.
Post-medieval generally refers to anything in the last 500 years and although witch hunting did occur from the time of the crusades (11th & 13th C), most of the British witch hunts which I suspect you are referring to reached peek levels between 1567 and 1640. The period known as the Great European Witchhunts occurred between 1450 and 1750.
Eventually I imagine we will be known to have lived during the second elizabethan times, but it is still Post-Medieval / Early Modern / Modern!
Even within the current post-medieval modern period we have Elizabethan (1st), Ind. Rev, Napoleonic, Victorian, Edwardian, World War, Inter War, World War (again), Cold War, Post-Communism (in Russia at least). Still, no point in waiting around for a new epoch!