Daytime refers to the period of the day when it is light outside, usually between sunrise and sunset. Some synonyms for the word "daytime" include daylight, day, diurnal, morning, afternoon, and the antonym of nighttime. Used in a sentence, you could say "I prefer to exercise during daytime hours when it's not too hot." This could be rephrased as "I prefer to exercise during daylight hours when the sun isn't too intense." "During the day" is another way to describe the time period from sunrise to sunset and is effective in getting the point across in a simple and concise manner.