I got approved for soft power (cooking) in HCMC relatively easy as I supplied everything needed upon application. If you search this group, many people have shared their experiences and what documents they provided.
Regards the 500k there is no specific time if needs to be in the bank. Many people have transfered it within days of applications and it was fine. I think people also upload 6months of bank statements with less than 500k to prove they've had the bank account open for a while and not just recently opened for this application