The reason the time of death is vague is because hermit crabs are generally lethargic creatures, at least in captivity. They do move about from time to time and engage in all sorts of activities, only at a slower pace. But sometimes they just hide in their shells (especially during molting times) and it's hard to tell that they are alive unless you pick them up and detect motion in the shell. They are extremely easy to take care of and require little time to look after. Just keep their food and water fairly fresh and clean the tank a couple of times a year and keep their crabitat warm and humid.
We had already buried a total of three hermit crabs and this guy was the last. He or she lasted nearly two years, but about a month ago it developed a strange condition losing its legs or claws one by one, until he had lost it all at the end. A Google search revealed that this condition is usually caused by stress and some crabs can recover from it, but others succumb to it and die.
This morning I buried the crab, complete with its shell and its severed last two legs, near the buried rabbit outside the house. the kitchen seemed emptier tonight without the crabitat but, as it is with all beings, death is inevitable. I think we did the best we could to make our hermit crab's final days as comfortable as possible.