According to USA Today, the coldest time of the day comes just before sunrise because the earth has had all night to expel the heat from the previous day into the atmosphere. As soon as the sun begins to rise, the earth will immediately begin to heat up once again.
The highest temperature during the day usually occurs during the late afternoon between 3 and 4 p.m. The sun is at the highest point in the sky at noon, and it takes a few hours for the atmosphere to heat up. The exact length of time depends on where a person lives and the time of year it is.