Ideally a week or two in advance of your launch. To get aquatinted with the community and join in on the discussion. Great article discovery here: typestudio.co/blog/product-hunt-learnings
They can do it whenever but remember that PH tends to rate votes from people with established accounts more highly. So for example, if Product 1 has 100 votes (but all from freshly created accounts), while Product 2 has 80 votes (but all from people with older accounts with more activity), they will actually rank Product 2 over Product 1.
@dogyun_jeong Seems to be age of the accounts and speed of upvotes per hour - probably just PH trying to filter out what they consider to be bot-like activity.
storly.ai