ok we'll all i know is you have to go to the very bottom right of your town just walk round there..
Hey cant u only meet wisp on monday nights?!!? thats what a lot of sites say...
when you find his "empty lamp" during the day, you have to find him at night. then he will go inside the lamp, and asks you to bring it inside your house to get your wish. i dont think you have to wait until 4am, i dont stay up that late. and i found him, but i forgot the time that i did. he's still in my house after a couple of days, since i didnt rub the lamp yet.
he would either: make all weeds go away, kill all cockroaches in your house, or give you an item not in your catalog
edit: you cant see whisp at first, he's invisible. but if you're close, he will tell you to come to him. and stop you if youre going in the wrong direction