Hi Kartik
You should have minimum 2 days for sightseeing around Munnar.
Major tourist attractions are - :
1. Top station
2. Eco-point
3. Photo point
4. Erivikulam national park
5 Blossom park
6. Horticulture Park
7. Kundala dam
8. few waterfalls
9. Tea Muesum Happy Travelling
There are few view points,tea museum,rose garden and you can visit the sanctuary nearby...if you are still left with some time,visit punarjani martial art and kathakali show.we loved it!!
Being a native of Kerala and visited Munnar 5 to 5 times in the past i can very well say that Munnar is overrated so as the resorts as well as hotels. if you are with a gang of friends i suggest you to travel 40 km from Munnar to Suryanelli and camp overnight in Kokukkumalai Tea estate for about 1800 per person including food. Trust me you will never ever forget the trip as it is the one of the highest point in Munnar and a heaven for people who loves to do trekking. The Sunset and Sunrise from the top are something out of the world. https://www.tripoto.com/trip/out-of-the-office-hiking-up-all-the-way-to-taste-one-of-the-best-organic-tea-in-india-5c56adab86674 Take a route less travelled and you will enjoy to the core.
These are all the places u can visit in Munnar and around Munnar: Mattupetty
Pothamedu
Devikulam
Pallivasal
Vattavada
Attukal
Nyayamakad
Meesapulimala
Chithirapuram
Lock Heart Gap
Kolukkumalai
Rajamala
Eravikulam National Park