In terms of length of service it hasn’t changed much but I am finding school years are starting to come into play a lot more (as our start point is year8)
18mth service for pre training & then minimum 3-6mths in rank
So for the start of the academic year
Year 9 - pre NCO training (all cadets) LCpls 
if I was permitted in the ATC 
Year10/11 - Cpl - approx 18month service,
Year 11 - Sgt,
Year 12 - Sgt & FS
Year 13 - FS & CWO
Really clear on promotion criteria & doing interview boards for Cpl & sgt where one of the questions is “how would you manage those who are unsuccessful”.
It makes things really transparent & the cadets & cadet NCO are strongly in favour of the process. It also reduces challenges from parents who can understand the process & may have to deal with disappointed cadets.
The Pre-NCO training is done on a cross the board clean slate basis so all cadets feel it’s fair & that they aren’t held back by past sins. It also allows us to expand our knowledge & understanding of the cadets in more detail & have a pool to promote from.
Ah now this question mainly applies to cadet SNCOs. I have the standard flt command structure for the Sqn of Snr cadet, flt cdrs, flt cpls.
The NCOs that need to put out to pasture / moved out of the development stream get posted to the HQ flt where they have a NCO role profile (stores, admin training etc) for them to do support functions & not part of the general flt structure of the Sqn.
Allows us to keep things fresh & avoid bed blocking so the cadets coming through can keep developing.