间 (traditional 間) is the sun (日) seen through a doorway (门) — sunlight slipping through the GAP between the doors. From that crack came 'space between', and then 'a room' (the space within walls).
间 means 'between/among' and 'room': 中间 (the middle — with 中), 时间 (time — the 'space between' moments, with 时), 房间 (room — with 房). It's also the measure word for rooms: 一间房 (one room). A beautiful, abstract character — it captures the idea of the space, or interval, inside or between things. You've now learned all three pieces of 时间 and 房间.
Sunlight (日) through a doorway (门) — the GAP, the space BETWEEN; a ROOM.
间 is the 'space between' — which is why 时间 is 'time' (the gap between moments) and 中间 is 'the middle'. The sun peeking through a door says it all.