.. I'm counting down starting from 10 minutes. So I need something I little more automatic.
so, all you want is some 'clock' counting from 00:10:00 to 00:00:00?
ok,
some work, but..:
create 600 'stills' (=if you want your clock to show secs...), charts, jpegs, containing your clock.
safe each still as '001clock.jpg', '002clock.jpg' etc..
use QTpro or Mpeg Streamclip, choose 'open picture sequence', select first still.. SC will open the 600 stills, choose 'Export as dv', proceed in iMovie..
other option:
there are 'egg cooking clocks' at versiontracker.com etc.
use screengrabber tools as SnapZ, Screenflow, Jing (=free)
other option:
iMHD6 plus some geethree.com plug-ins offered 'clocks' ..
it is no problem to create a movie, your problem is to create the clock 😉