Hi Arkka, One day is enough to explore full darjeeling.
Second day you can relax with nature.
Toy train, tiger point hill for sunrise, darjeeling zoo, tea gardens, Japanese peace pagoda are some places you can visit
1st day book a Cab for side seen like Darjeeling Zoo, Batasia Loop, Rock Garden, Lamahatta, Tin-Chulay tea states, etc. 2nd day book a Joy Ride with Heritage Train on 1st half..and on other half spent your time at Mall.. If you are a foodie, try some restaurants like 1. Sonam's kitchen (breakfast)
2. Glenary's— Bakery, Resturant & Pub (Breakfast and Dinner)
3. Keventers (Breakfast)
4. Kunga (Dinner ) you should try those restaurants..