Please note: Short Term Medical (STM) coverage is not a replacement for ACA mandated health insurance. It is solely meant as temporary coverage to provide you some financial peace of mind until you are able to enroll for ACA qualified coverage.
Day(noun) the time of light, or interval between one night and the next; the time between sunrise and sunset, or from dawn to darkness; hence, the light; sunshine. Day(noun) the period of the earth's revolution on its axis. -- ordinarily divided into twenty-four hours.
A solar day is the time it takes the Sun to return to the same position in the sky. The exact length varies slightly over the course of the year, because the Earth's orbit around the Sun is not perfectly circular; the tilt of the Earth's axis with respect to its orbit also has an effect. See the linked article for details.