How long does a JD (law school) take if you have a master's?

I currently have a master's in financial planning. However, I am able to take advantage of some tuition reimbursement at work and I am considering a JD (and eventually an LLM in taxation). How long will it take to get the JD considering I already have a master's degree? Does it even count towards anything? I will be attending part-time since I will be working during studies.