Western Governor's University is completely work-at-your-own pace, so you can accelerate it if you choose. I know many people who have completed their RN to BSN in less than 6 months. The best thing is that you pay per semester (each semester is 6 months long), rather than per class, so if you can complete it in 6 months, you will only pay for that semester, regardless of how many classes you take during that time period.
The drawback of WGU is that their grading is done as pass/fail, rather than letter grades. A pass is considered to be the equivalent of a B, so it will look like a 3.0 on a transcript. If you're looking to matriculate into a competitive graduate program, this might hinder you.