시간 and 틈 both mean "time". 1. 시간 means "time" only 시간이 없다 - There is no time 2. 틈 means "time" and "space". 오늘은 틈이 없었다 - There was no time today 의자와 책상 사이에 틈이 있다 - There is the space between a chair and a desk. 3. 공간 means "space" only 저기에는 공간이 없다 - There is no space. I hope my explanation will be helpful to you :)

틈 think of it as a gap both in the sense of time & space

Hi It is my first answer for studying Korean people. Maybe you like Shinee, I know that because I search your question in the google. In my opinion, 그 긴 시간 틈에 = 그 긴 시간에 roughly same meaning. From the context, 닫혔던 너의 창에 그 긴 시간 틈에 겨울 가고 봄이와, 틈 is time difference. I hope you can understand that.