안녕하세요. :) 1) 집에 오니까 ... 집에 오니까 밤 12시였어요. > 집에 온 후에 시간이 12시라는 걸 알았어요. I got home and then I realized the time was 12 o'clock. I didn't know the time before I get home. 
 책을 읽어 보니까 재미있었어요. > 읽은 후에 재미있다는 걸 알았어요. I read the book and then I realized/knew it was fun. I didn't know it is fun or not before I read. 김치를 먹어 보니까 조금 매웠어요. > 먹은 후에 맵다는 걸 알았어요. I ate Kimchi and the realized it was a little bit spicy. I didn't know it is spicy or not before I eat. 2) 집에 왔을 때 ... 집에 왔을 때 밤 12시였어요. When I got home it was 12 o'clock. It simply says the time when I got home.