Sleepovers are pretty much weekend only things with us (and seemingly everyone at our school)
I don't know that we'd be categorically opposed if a kid needed a place to cover a parents absence or something like that, but that seems different than a "sleepover" there's a connotation of a fun night had by all, in that term.
So, yes, we'd house a child on a school night if needed, but a fun sleepover, no that's weekend stuff.