Different cooking times for red and brown lentils?
You likely won't find a definitive answer out there, as there's a range of times for the lentils.

To summarize an article from the Washington Post :


Red, orange or yellow split lentils : 15 to 25 minutes
Black beluga lentils : 20 to 25 minutes
French du Puy lentils : 25 to 30 minutes
Brown or green lentils : 30 to 40 minutes


... suggesting that you'd need to add the brown lentils 15 minutes before the red lentils ... but you mentioned that you cook the red lentils for 25-30 minutes, suggesting that either you like them to fall apart, or you're cooking over lower heat.  If it's lower heat, I'd give the brown lentils a 20 minute head start.

If that's going to put a crimp in your timing, I'd suggest starting the brown lentils in water (or some flavorful liquid), and cooking for 15 minutes while you're getting everything else together, then draining and adding them at the same time (or shortly after) the red lentils.