Like a white colt flashing past a crack - time flies.
Tips
culture
驹 specifically denotes a horse under two years old. It anchors the famous chengyu 白驹过隙 'a white colt darting past a crack' - Zhuangzi's metaphor for the brevity of human life.
memory
马 (horse) + 句 (phonetic) - a small horse that is just one sentence (句) long, not yet a full grown stallion.
Horse radical on the left fixes the subject: 驹 names a young horse - specifically a colt or foal. The radical groups it with the rest of the horse family: 驴 donkey, 骑 ride, 骏 fine steed, 驰 gallop.
Right side supplies the sound: jù to jū (tone shift). 句 is a pure phonetic here with no semantic contribution. The same phonetic anchors 拘 detain, 局 office, 桔 tangerine - all sharing the jū/jú/jù reading cluster.
