it's about 40 minutes, perhaps less if you catch the express train.

the station (fr: Gare) for RER and TGV is located between halls 2C and 2E. this is quite easily walked but there is a shuttle bus circling terminal 2 (landside) as well.

you'll want to be careful with the timing and also keep a close eye on your belongings to avoid being a victim of a "grab and dash" theft. the trains run often in the morning, though.

bon voyage,
benzguy80