The temporary penalty put on your skills and attributes after your death is not a thing that will stay there for a certain period of time. To get rid of these death penalties, one must get new experience points, which will not only help his character in raising up other skills, but also will diminish any death penalties his character may have on it. This means those penalties will stay on your character for an undefined period of time if you stop gaining experience, but you can get rid of them extremely fast if you're not sitting down and waiting, but going on and continuing to earn XP, no matter if by killing monsters, other players or completing quests.