I would say at best you'll be an hour late. Like the previous poster said it's about a 90 minute drive with no traffic whatsoever, and that never happens. There's always traffic through the city, and there may even be traffic through Napa as you head up to Yountville. That assumes you get off the plane right away, no baggage, flight is on time, etc.

I'd go enjoy it another time! For such a special meal I wouldn't take this big a risk. You don't want to let a big penalty ruin the experience for you or your friend.