With an economics background, you could potentially practice patent litigation (with a law degree), or work for a firm that provides damages calculations/expert testimony for patent litigation (or other types of litigation). Capanalysis is but one example of an economics firm that provides litigation support services, including IP litigation support.
Regarding how long is too long before returning to school, it all depends on personal circumstances. If you are single, have no kids, and relatively few financial obligations, than returning to school is a piece of cake. Once you start piling on personal or financial responsibilities, it becomes much much harder. From personal experience, I can say that going to law school while working full time is not an easy road . . . one I would not take if faced with the same choices again.
The long and short of it is that the sooner you go back to school, the easier it will be.