Although we had afraid but drive well and reached Delhi at 10:30PM night in same day
The road is completely safe. From Delhi to Chandigarh, it is a straight National Highway. A very good road. Delhi to Chandigarh would take you 5–6 hours. Then, you'll come across an amazing curvy highway, the Himalayan Expressway till Parwanoo. Parwanoo is where the altitude starts rising. Here, you'll find the curvy roads. An easy drive it is, well, not really. Currently, construction is going on this road as the Himalayan Expressway is being stretched further, so you'll find a lot of traffic. You'll enjoy the views for sure. And from Dharampur to Kasauli, it is a fine road. It will take you around 2 to 2.5 hours to Kasauli from Chandigarh. There are a lot of eateries in Jabli and Dharampur, so you can fill your tummies. ;)
Enjoy your trip.