I can't say I disagree with upgrading to an MBA rather than go for another degree. However, I don't know what your employer is willing to cover, and if that's all he will cover, then go for it. Any reasonably educated employer would realize that two separate degrees can be more work. Although, really, it's usually about the same about of work for most people.
Also - you say you have a political science degree. why not law school? That's one of those majors pre-law students choose. Finishing off at a real instituition is also a VERY good idea. Employers can be iffy (especially in traditional areas) about online degrees. Online courses -they can handle, but online degrees -maybe not.
Online classes stretch your time and abilities in different ways than regular classes. While regular classes start, end, and give homework, online classes are very much like constant homework. (Read section, work problems). You may find yourself doing the work in odd time slots or periodically. That's ok as long as you can keep those odd time slots consistent/not spotty. Flexibility in online courses isn't really about time at all. It's about the freedom to choose when to do it, where to do it, and how to do it.
