expression
in spare moments; between tasks; whenever there's a break
Used adverbially, often with に, to describe doing something during the gaps in one's schedule or while waiting. Implies using small pockets of free time productively.
仕事の合間合間にストレッチをしている。
I do stretches in the spare moments between work tasks.
合間合間に単語を覚えるようにしている。
I try to memorize vocabulary whenever I have a spare moment.