When to use for a long time in Korean
Korean: 오랫동안[ o-raes-dong-an ]

When to use it
오랫동안 means "for a long time." Use it when something continues for many minutes, hours, days, or years. It is common in everyday sentences like living somewhere, waiting, talking, or studying for a long time.
Example sentences
저는 이 집에 오랫동안 살았어요.
I lived in this house for a long time.
우리는 학교에서 오랫동안 공부했어요.
We studied at school for a long time.
밖에서 오랫동안 기다렸어요.
I waited outside for a long time.
친구하고 오랫동안 이야기했어요.
I talked with my friend for a long time.
가게에서 오랫동안 옷을 골랐어요.
I chose clothes for a long time at the store.
부산에서 서울까지 오랫동안 버스를 탔어요.
I rode the bus for a long time from Busan to Seoul.