With regards to the Navy Nurse Corps, for a generic BSN you get 1 year of military credit for every 2 years worked or spent pursuing a graduate degree.
Military wide pay grades O-1 and O-2 are 2 years each respectively. Meaning that you must have a minimum of four years experience (since obtaining your BSN) on the civilian side to come in as an O-2 and 8 years to come in as an O-3. From what I have seen the Navy does not waiver from this formula.
It is my understanding that bonuses are offered only to critical wartime specialties. CRNAs of course for advanced practice Nurses and ICU, ER/Trauma, Perioperative nursing, and possibly med/surg for BSNs.
I do not know what formula the other branches use; however, a friend of mine with prior service and many years as an ADN prior to obtaining his BSN went into the Army as a senior O-2 (he only had his BSN for about a year prior). I know that with the credit he was given he was just shy of O-3 and probably made it before leaving his officer basic course.
Keep in mind that he was a Navy E-5 Fleet Marine Force Corpsman in Baghdad with at least ten years enlisted service just a few months before reporting to San Antonio and he looked like a "Mexican General" with all of his ribbons on his chest. E-5 to O-3 in less than a year, not bad!
Additionally, if you have 3 years prior enlisted sevice you earn a nice bonus in your pay each month for that service. An O-1 friend of mine with 10 years enlisted service makes about what a junior O-4 without prior enlisted service would make, again not bad!