Definitions for daylongˈdeɪˌlɔŋ, -ˌlɒŋ
Random House Webster's College Dictionary
lasting all day.
Origin of daylong:
lasting through an entire day
daylong, all day long(adverb)
during the entire day
"light pours daylong into the parlor"
Throughout the day.
Which lasts a day, or approximately so.