This is a difficult example to use as the sentence itself doesn't make a lot of sense at the moment. Can we change it a little so that we have a better example to look at?
1. I work fewer hours than any worker at the biscuit factory.
2. I work fewer hours than a worker at the biscuit factory.
Both these sentences now mean the same thing - they also mean that you don't work at the biscuit factory yourself.
If you want to compare yourself with workers at your place of work (let's say the biscuit factory)
1. I work fewer hours than any other worker at the biscuit factory.
Sentence 2 cannot be made to work in this context.