If you include research, planning and reading...
probably an hour a day at present. And I am about 6 months of starting the build.
Once I am in the build cycle I envisage 1-2hrs avrage on week nights and a few more on weekends. Incresasing once the chassis is welded and I can get my ( by the time it's ready ) 6yr old out to help with the fitting up.
Big problem is that I will be heavily into the planning and delivery of the I.T. systems for our new Building that opens in Jan 2011. Which will leach all my spare time and energy.
TT