Probably just under three months time at a guess. It takes about 8 weeks to control covid new infection numbers if the outbreak is small and with prompt action like Singapore has done. Then you need a two weeks of less than 5 unlinked cases per day. HK is OK at the moment - we had two potential outbreaks that were very quickly controlled just after Chinese New Year - very fortunate to have had it controlled. If vaccination numbers go up (Singapore is leading HK but both places can do better(!)) then perhaps even less than three months for the travel bubble to appear. There’s definitely political support on both sides for a travel bubble to get going. For comparison, Taiwan has less than 1% of the population vaccinated and is currently experiencing a very worrying scenario of active community infections.