Proper training in Motion can save you unbelievable amounts of time and headache.
For motion graphics, it is always good to pre-plan it first. Sketch it out first. But some folks just dive in and hit things until something works.
As for workflow, there's no set in stone workflow to create what you're discribing, just import all of your assets, and start configuring.
I do presentations quit often, so here's what I'd do.
I'd make the Motion project an exact time, like 10 minutes on the nose. Export as an H.264 file. Bring that into Keynote and make the slide it appears on automatic. Here's what I mean.
Place the timer QT movie on the slide. Set it to play autiomatically after in starting transition. Then set the transition to the next slide to be automatic after 10 minutes, and something like 3-4 seconds extra. Those seconds go by slower than you'd think. So as soon as the timer is up, perhaps also add a chime audio file to that slide to play 10 minutes and 1 second after the movie starts. Then the timer hit's zero, the chime sounds, then it automatically changes to the next slide. That would be cool. "Look ma, no hands!"
So, any of those generators, depending on what you want it to look like. Keyframe them to start at 10 mintues, and count down to zero.