Moment's Leisure, Free Minute
noun
You have a measurement (3.03 cm!) of spare time. This isn't much free time, but it's a free minute that you have.
すんか
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
夫は、いつも寸暇を惜しんで働いています。
My husband devotes every spare moment to working.