It has been answered
4 years unless it is within the base area.
However, over the next 5 years there are 300 captains who will reach 55. They can only continue to work in HKG past 55 if they are in C+T. If they want to continue on the line they will need to get a basing as it is RA55 in HKG.
At the moment we have 100+ CNs based in EUR, 100+ based in US(incl Can) and 50+ in Australia.
Out of that 300 due to retire, around 250+ (assuming around 15% are C+T and stay in HKG) will be seeking basings. Now, bear in mind that no CN already on a base will need to retire for another 10 years thanks to onshoring/RA65.
So of the 250, about 75+ Aussies, 50+ brits and 60+ US/Canucks will be looking for basings. Given the numbers already on basings that would mean that it will be difficult to get a basing...remember, no one needs to retire now on a current basing for another 10years!
Now imagine you are a senior FO on a base looking to get your command in HKG. You will have to take the command knowing full well it is highly unlikely you will get a basing within 5-10 years as a captain. At current exchange rates you are close to command salary anyway (obviously ignoring tax and pollution!). SO the net result is that FOs are probably not going to rush back to get commands. And if any slots do come up it will be the 8-10 year FOs taking them whilst they wait another 3-5 years for their command slot to come up.
So, 4 years or 14 years, do you really think anyone junior will get a basing once CoS08 is introduced???
I hope that has answered your question on inter-base transfers!