How important are product hunt upvotes in the first 8 hours?

The most important In first 4 hours order on the launch page is random Then products get sorted by # of votes If you will be down the list after 4 h, you wont get much visibility for people who come to visit launch page

Important-est! First 4 hours, important-est pro max!

After 8-10 hours, traffic reduces. So these are the most crucial hours on your launch day.