A picnic bus starts at 8 am at constant speed 40 km/hr for 3 hours.The picnic place is at a distance of 120 km.The whole route is a straight path. After some travelling rain starts due to which the driver decreases the speed to 20 km/hr upto the time of raining. When rain fall stops he increases his speed to 1.5 times and reach the destination on time.

What will be the duration of time ?