Additional pet rates for duration based services needs an overhaul

I have 4 services set up that are duration based services. The price depends on the duration chosen - 4 hour, 8 hour, 12 hour daycare. When going into the additionall pet rates for these duration based services I can only input one price so even if someone chooses my most expensive daycare duration as their service, their second dog would be charged at only $15, as an example. Somehow there needs to be additional pet rates for each of the durations. Hope I am making sense? How is everyone else handling the additional pet rates for daycare/duration based services?