Outside of rush hour

• Not at the time of highest demand
• Going to arouse, picked up when it's not so busy
• Time of few users
• Reduced-price, most likely
• Like late-night commuter trains
• At a time when demand is less
• Not the busiest
• Non-rush-hour, say

Wiktionary Word definitions in Wiktionary
a. (alternative form of off-peak English)