Day-and-night is a term used to describe something that is continuous or without interruption. Some antonyms to this phrase could be sporadic, intermittent, or occasional. Sporadic means something that occurs at random or irregular intervals. Intermittent refers to something that stops and starts repeatedly, while occasional means not frequent or regular. Other antonyms for day-and-night could include fleeting, short-lived, or temporary. These words suggest something that is not constant or lasting, but rather brief or infrequent. Overall, antonyms for day-and-night imply a lack of consistency, regularity, or continuity.