"It depends," Hermione says, sounding apologetic. "Anywhere from minutes to hours, depending on how strongly you cast the spell. There is a spell to wake up Stunned people, but it doesn't have to be used."

She pauses. She can see the idea's unappealing- rather understandable- and tries to help, adding, "Really, think of it as like a blunt weapon. It's magical, but it has the same effects as somebody hitting you with- well, anything else, really. You just have to get out of the way fast. The fact that it's magic doesn't really change that."

And she's assuming, she realises, that Steph knows these things and can fight- she must, after all, be asking for a reason.