At my place the policy is a 30% deduction if up to 7 days late, and it's up to the marker to apply it.
I wouldn't apply it for being 3 hours late. When we get to, say, 12 i might think about it.
Plus, you don't get marked down for mistakes. You get marks for what you did. If referencing is worth, say, 5% then if you do it right you get the full whack. Mostly right and you'd get 3 or 4. No references no marks.