Two strokes are usualy gone in a day or two-three at most.
Four possibly a week but no more.
Six is a different matter entirely.
A moderately hard caning will leave bruising for about the same length of time as four-maybe a little longer.
A severly hard full force caning will mark you heavily for a good two weeks.
However,all boys,and girls,mark differently-some people bruise a far lot easier than others so,at best,you can only talk in averages.