An echo is the reflection of sound. The speed of sound in air depends on temperature: higher temperature means faster sound speed. The formula is $v=331+0.6T$ m/s, where T is temperature in °C. In summer, air is warmer, so sound travels faster. Therefore, the sound wave reflects off the surface and returns to the listener more quickly. The time delay for the echo is shorter in summer compared to winter.

Final answer: Sooner than during winter