From what Im understanding, her sister is coming into town for 4 days so if she wants you to have this child as well as her own then it would seem to me that it is so they can spend some time together. To require a 6:30 pick up so they can socialize is just disresptful tou you and their children when it is a want rather than a need. I would charge a higher fee because the sister will be getting a premium service of drop in care but I wouldnt let them pick up later than 5 if all they are doing is catching up.