Great question, probably no real answer for now until the work starts, from what I can see ... Looks like the variables are definitely first how many people will be affected, how they choose to go through local streets as detours, the method with which the detour will be conducted, or whether ferries will be added, and how curious the drivers are throughout the project. There is no 'estimated' commute time increases that I can find. Probably credit to the fact that no officials are willing to be quoted. :-)
I did see a quote from representative from NAPA county saying that it's goiong to be 45 minutes in traffic for three years. Where the number came from was not explained. could very well be a random comment.
Here are links to a couple articles: