Not tried to get into LM by car on a Saturday morning myself, not a masochist
However viaMichelin reckon it's 2 hr 38 from CDG to LM.
That time is based on keeping near the speed limits, and no delays a toll booths.
Others with experience of the route might disagree, but I would add at least another hour to your estimate, prehaps 2 or more.
2 years ago it took Andy 1/2 hour to get from Arnage village back to the circuit, on a motorbike!