Upvote:4
Is it sufficient,
Not really. If everything goes super well, you might make it but in my opinion it's extremely risky.
Can this flight likely help me catch the train from HK
Sure. Taking an earlier flight will certainly help but it's in no way guaranteed. I personally would not do that either. Border controls can be very slow and are notoriously unpredictable. Covid adds a lot more uncertainty as well.
Here is another option:
You can avoid Hong Kong by taking the ferry to Shenzhen (or maybe even Guangzhou ) At the Sky Pier at the airport you can enter the mainland directly without having to go though Hong Kong. In Shenzhen you can spend a night and then grab a train to wherever you want to go the next day.
Upvote:4
Let's imagine our flight arrives on time, and the aircraft door opens right at the scheduled time.
I'm not counting anything Covid-related because I have no idea what the current procedures are or how long they take. I'm not counting your side trip to get a new test done either.
So it could take up to 2h39 from aircraft to train.
So, no, 2h27 is not feasible, and 3h27 is probably cutting it very very tight.
And, again, that's:
The usual recommendation for a self-transfer within the same airport is at least 4 hours (when missing the second flight is not too much of an issue). Here you have a lot more travel and formalities on the way. Either get there much earlier, or plan to spend the night.