Using a unique time-diary data set (tracking every job and every childcare arrangement from the time the mother gives birth until the child reaches age 3) through the Fragile Families study, this report describes the prevalence of nonstandard-hour work schedules among a primarily low-income sample of working mothers with young children. Consistent with past research, the Fragile Families data show that nonstandard-hour work schedules are common and that informal childcare, such as grandparents and fathers, is often used. The Fragile Families data revealed that more than half of mothers who worked a nonstandard-hour schedule at some point also worked with a standard-hour schedule in the first three years after giving birth. This schedule instability was associated with job changes rather than schedule changes in the same job. (author abstract)