Short answer (from a Watts grad): the fastest this program can be completed is 2.5 years (1 semester of UMO, 4 semester of the nursing portion).
The whole 18 credits can potentially be done entire online if you have all the prerequisite requirements, but they may make you take A&P in person at Watts. They usually require the 18 credits to be done the semester before you enter the nursing portion. I.E. if you start UMO in January, you will start Watts in August and if you start UMO in August, you will enter Watts in January.