The rice and dal both need to be cooked, but the grains of the rice need to be separate and dal not mushy.
After the first whistle, dal should be 80 percent cooked.
Pressure cookers vary, you may have to adjust water as well as the time, how soon you open the pressure cooker after the whistle.
Dont soak rice as it could overcook.
If you are not sure about cooking in pressure cooker, once dal is cooked, transfer cooked dal into a pan, add rice, bring to a full rolling boil, and cover and cook for 7 minutes on simmer. Open lid and separate grains.