After the Nursing Officer study (about three years ago) there was a massive change in rank structure and employment model. All of this below applies to the Regular Force only. HSO as a occupation has died back a few years ago, in around the time of the nursing and HCA study which ran concurrently.
You commonly see now post graduation / RN:
Years 1 to 3 years - Lt - There are no 2Lt Nursing Officers, less some very rare situations.
Captain - some stay at this rank forever as it is competitive to get to Major. It is the working nurse rank. If you want to do clinical work as the bulk of your work then this is the rank to be.
Major - You can do this as fast as 5 years as a Captain now if you are awesome. There are way more of these in the past (40) and they seem to be everywhere. Some are clinically focused (specialty practice leaders) Many say they do a lot of clinical but do not because of the workload of being a Major leading other nurses / things. Nurses at this rank can complete for "Regulated Health Officer" positions against Pharmacy, Bio-science, Social Work, Physio, although there are not many of them to complete for (if any currently).
LCol - I think there are like 6 of these. Quickest you will see this is likely 7 years as a Major if you were a superstar, but likely much longer. Very competitive. Nurses at this rank can complete for "Regulated Health Officer" positions against Pharmacy, Bio-science, Social Work, Physio. I think one has done that so far for a year or two and then returned to nursing jobs.
Col - There is one full Col now - the Chief Nursing Officer double hatted as the COS for DGHS-Clinical. Nurses at this rank can complete for "Regulated Health Officer - DSA" positions against Pharmacy, Bio-science, Social Work, Physio - but none have done so yet.