I think you need to be firm but also tactful. Maybe smile and say something like, 'it's been so nice having you here, I really have enjoyed it, of course I realize we all have lives to get on with, but before you leave we must make plans to meet up again.'. Or maybe say you have been making plans to decorate a certain room, and so 'it was so nice you could stay before I decorated, it's going to be so messy for the next week or so, but I'm so glad you came'. If you use the right words, you will get what you hope for and no-one's feelings will be hurt.. if they still don't get it, then you have to just say, 'I really need you to leave now because I have to ....' and then list all the things you need to do