how long to boil rice for Biryani?
Different rice varieties have different cooking times. This is how I do it.

Wash and soak your rice according to the packet instructions (usually about 20-30 minutes).

Bring water to boil in a big pot (I use roughly 3 litres of water for about 1.5 cups of rice). Once it starts boiling, add the rice and the required amount of salt (I use about 1tsp for 1.5 cup of uncooked rice).

Boil the rice on a high heat until it is about 70-75% done. Check its doneness by holding a grain in your hand, it should be hard enough and only be mashed when you press on it firmly. Remember, it's going to be cooked again in the steaming stage when you layer it with the gravy, so you don't need to fully cook it. The grains should still have a slight bite to them.
Another way is to judge it visually. The uniform solid color of rice starts to change as they cook. Rice grains cook outside to inside, which means the outer part of the grain starts becoming translucent first as it cooks while the inner part of the grain still remains the solid color. You should be able to see a thin line in the centre of every rice grain. This is where you want to stop the rice from cooking further. It takes a bit of practive to be able to use this visual method but you can estimate the % of doneness this way.

Drain the rice immediately to prevent overcooking.