Does a sentence-ending 'respectively' always have a comma before it? E.g.: The three jobs took 5, 12, and 4½ hours, respectively.
Yes, a comma is needed. But the way you use "respectively" is incorrect in this case. You need a parallel list to be able to use it. For example: "Job A, job B, and job C took 2, 3, and 5 hours, respectively." In your example, the order of the three jobs is unclear, so unless the jobs are listed in order in the previous sentence, you'd need to use a parallel list like I did.
