Roger had a maximum of twelve days to live.
The doctors had calculated his expected life span based on a number of important criteria including his weight, his urine output, and the size of the tumour on his kidney.
Granted he had done some research on his own -- the internet is such a valuable tool -- and considered the doctors' calculations to be off by at least fifteen hours, give or take sixteen minutes.
As a good scientist, he decided to use his time in the utmost of utilitarian fashion. He broke down the days into four hour segments, and assigned a variety of tasks to each segment. The more pedantic items were accomplished first: the catering and urn selection at the funeral home, the beneficiary and executor finalizations at the lawyers' office, and, of course, the appropriate adoption protocol for his cat, Fluffy, to ensure her continued life. After all, he could not possibly die and leave Fluffy's life in the hands of animal shelter workers who would just as soon euthanize her than find her an appropriate adoptive placement.
The hospice workers worried that Roger would have fewer than twelve days to live if he continued to work so fiendishly on his to-do list. However, he had decided that he would end his life just as he had lived it so far, with his nose pressed ever so firmly against a grindstone, metaphorically speaking, of course.