Though there is no hard and fast rule regarding whether it is better to drive in the night or day time, I prefer driving in day light due to various reasons.
My suggestion would be to plan your journey such that you reach Munnar in the day time before 4PM in the evening.
There are few check posts in this stretch and at each check post you will have to pull over and go to the guard room and write Driver Name, car registration number, number of passengers in the car, from where you are coming, your destination in the register kept at the guard room.
The duty officer may come and inspect the car as well. It is illegal to carry liquor across state borders.
That’s because your destination is situated approximately 1800 meters above the sea level in the Western Ghats.