build timing

[Alex in the Studio]

i think a reference to this page should be included on the build
instruction page.  having a reasonable expectation of how long a build
might take has an impact on scheduling.

for example, i began this build 3 hours ago and i am leaving for chicago
this evening in another 4 hours.  if it hasn't finished, i will be
forced to abort in the middle.

cheers,
alex