how long should it be?

well, amidst the pressures of composing 101 things to do in 1001 days, i happened across this site as i was looking for guidance with the 10 short stories i've proposed writing. i've never thought about how long a piece needs to be, apart from assignments i've been given. but here i am, looking for answers. though this website has an awful pink hue remeniscent of pepto bismol, i think there's probably a little here and there to be gleaned from it.