When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear an echo sound on a hotter day?

Speed of sound increases with temperature. Hence, on a hotter day, speed of sound in air will be more.

An echo is heard when the time interval between the reflected sound and the original sound is at least 0.1 seconds.

Therefore, on a hotter day, as speed of sound in air will be more, for same distance, time taken by the reflected sound to reach the ear will be less. As chances of this time interval being less than 0.1 seconds is more so we might not hear an echo sound on a hotter day.