。
I don't have time to travel.
Literal
Travel do free-time [subject-が] doesn't-exist.
暇がない (don't have free time) uses 暇 (free time/leisure) with がない. 旅行をする暇 = 'free time to travel' — the verb + 暇 pattern indicates time available for an activity.
。
I don't have time to travel.