Thanks, Jesse, now I see that inside the build view there is a way to see when
the build started. Another possibility for me was to look at build timestamp and
try to calculate the duration, but then it got really tricky when different time
zones are involved.
So, yes, a simple note with current build duration should
do the trick just fine.
> Perhaps you mean somewhere near the progress bar? Like as a hover tip?
Yep, somewhere there. Maybe a hover tip, if the info does not fit into the table
to the right of the progress bar.
An idea with color coding seems to be nice too, but I could live without it 
AFAIK on the job page there is a notice such as "Started 24 minutes ago".