(PS - why didn't the clock start after Rivers got sacked and the Saints declined the illegal motion penalty? Since when can an offensive penalty help the offense with the clock.)
The illegal motion penalty was on the bad snap (not the sack). I'll go back and look to see if I can figure out what happened with the clock.
FWIW - It was a 7 yard loss, but not a sack, it was an aborted fumble (bad snap by the center), recovered by Rivers. I think because it's considered a fumble recovered by a different member of the offense the clock stops.