Time to command is impossible to pre determine. There are a core group that will never leave (probably too burnt out to bother!) and there are the remainder who are more motivated career wise. I would say they comprise about 50% of the total. If they turn over quick then command comes quick, it all depends on whats on offer elsewhere. At the moment it appears theres a lot on offer and Qlink (sunnies and eastern) doesn't offer career progression, just some meagre attempt to sway a few to stay in the hope that it will slow the flow to a more manageable number.
It should come as no surprise as it's a time honoured tradition after all and plenty fall for it first time round.
SN