How long does it take for a review of documents?
I suspect you know the answer to this - no-one knows, and it's not about how long it takes them to review the documents, but how long it takes them to get to it (how much other stuff they have on their desk/other urgent matters). And then after that - what matters to you - how much time to get/issue final decision and issue e.g. passport request (assuming of course they don't want something more).
So might be fast, might not. Most important thing is that HK seems to be moving and not closed due to covid.