Well, many preworkouts will differ in the way they work, so it is hard to tell exactly – all of them will have different ingredients with differing ratios. I think that it would be rather safe to say that they will last 2-3 hours. At most 4. But definitely not for an entire work shift. Perhaps you should consider having a good meal rich in protein before going to work – this energy will last you for long. Also, buckwheat has a very long lasting energy boost, so it might be a good idea as well.