The time Necessary to break a password:
Count the number of possible characters and raise to a power equal to the length of the password.
So, C = Possible characters and N = length of the password therefore:
C^N = the total number of possible key spaces available.
As you can see by the chart, it doesn't take long for the number of possibilities to reach a large number of possible results and the larger the pool well... The longer it takes to finish.
So Dave is working on a car. That car let's say conservatively, has 100 decisions for Dave to make about it's completion. Each decision so far, has had at least a half dozen possible outcomes. So 100 ^ 6 is 1000000000000. We can reasonably expect Dave to make these decisions in a timely manner (according the chart) of somewhere between 8 days and a year. Not too shabby but this is just decision making, not actual construction.
Now Dobby is back in the mix. You would think that you'd just take the number from each car and add them together and have a result that is twice as big as the previous one, right? No.
Instead of 100^6, we now have 100^12
I think we might be in the range of over 76.11 Billion years to finish both cars.