I found this thread from last year where people were discussing their dependent visa renewals: https://geoexpat.com/forum/54/thread338296.html
One person said: "So I got into town and they accepted my passport and HKID card and told me to come back in 3 hours. Long story short after a little bit of running around and paying my fee they renewed it for 3 years."
Another person said: "I am from Southeast Asia, but I just need less than 1 hour from time to hand on apply my document to the time I received my new visa (3 years more)."
However, on the official website, under processing time I see:
Extension of Stay | Immigration Department
"Routine applications will normally be finalised within two to three weeks upon receipt of all necessary documents."
Does anyone know how it typically works? I'm out of Hong Kong right now, and planning a trip back specifically to renew my dependent visa, and I'm trying to figure out how much time I need to be there.