As soon as
This structure indicates that one action occurs almost immediately after another, often suggesting a brief time gap.
Examples
彼は部屋に入ったか入らないかのうちに、子供たちが騒ぎ始めた。
As soon as he entered the room, the children started making noise.
彼女は名前を呼ばれたか呼ばれないかのうちに、振り向いた。
As soon as her name was called, she turned around.
この仕事は終わったか終わっていないかのうちに、次が来た。
As soon as this job was finished, the next one arrived.
Quick check
彼は部屋に入った___入らないかのうちに、子供たちが騒ぎ始めた。