Call them. Ask. That's the only way to really know.
But if you're going with the dealer it's going to be at least $200 more expensive than it needs to be. I'd say they'll probably charge anywhere between $200-$500, maybe more. And the time it'll take can be anywhere from half an hour to a week. It really depends on whether they have that mirror on hand to replace the broken one (unless the damage is VERY minimal I don't think they bother with fixing, they'll just replace). IF they have the part on hand they can be very quick, I'd give it an hour tops, unless there's damage to the paint on the car near the mirror or anything. If they don't, it may take them one to two weeks to get it in and then fix it. (I had to replace a fuel line on a 97 GTP and that took a week plus a day to actually come in)
Anyway. I'd suggest fessing up to your dad, telling him you're SUPER DUPER REALLY sorry and offering to pay for the damage before he gets a word in edgewise. I know it sucks hard when you break something you know your parents are going to go ballistic over but it's really better to just fess up and take what's coming to you sometimes.
HELP PLEAASE