The time from Joining the RN to going frontline is going to take some years.
You join BRNC Dartmouth and do 9 months there, including 3 weeks flying grading with 727 Sq at Roborough airport. This is now done i your first 14 weeks to make sure neither yourself nor the Navy are wasting their time.
Having passed out from BRNC you will start DEFTS at RAF CRanwell within a few months. 6 month course there then get selected for fixed wing or rotary.
If fixed wing expect another couple of years (not including holdovers before getting onto an Operational training squadron.
If rotary you do a course at Shawbury then get streamed onto helo type. Join Advanced/ operational training sq, pass course, get wings.
For helo expect about 3-4 years from joining to frontline.
For fast jet make that 5-6 years.
Return of service is 6 years for both routes, you are guaranteed an Initial Commission for 12 years when you join.
Hope that helps.