D.W.
Maybe I'm naive about the medication but doesn't it last for a while? Or does it take awhile for the medication to take effect? Either way, I don't see where there is a "snap to it and get excited" aspect to it. My husband and I actually enjoy the idea of "scheduling" sex. We have to young children and it gives us something to tease each other with and look forward to at the end of the day.
I think this is probably a much deeper issue than scheduling sex. You have surely been through a lot with your husband's diagnosis. Have you considered counseling sessions with a sex positive therapist to vent some of your frustrations in having to deal with his illness all these years. You owe it to yourself to be in a good place as well.