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 echo sound on a hotter day?

An echo is a sound caused by the reflection of sound waves from a surface back to the listener. It is heard when the time interval between the original sound and the sound reflected is at least $0.1\mathrm{s}$. 

It should be noted that, 

               Speed of sound (v) in a medium is directly proportional to the temperature (T).

                                                                 $v\propto T$

i.e., as the temperature increases, the speed of sound in a medium also increases.

Since, $\mathrm{speed}, v=\frac{\mathrm{distance}, d}{\mathrm{time}, t}$

                                                               $\therefore \frac{d}{t}\propto T$

Hence, the distance will be directly proportional to temperature of air and time will be inversely proportional to the temperature.

So, on a hotter day, the time interval between the reflected and original sound will decrease and an echo is audible only if the time interval between the reflected sound and the original sound is greater than $0.1 \mathrm{s}$.