noun
work day; day of attendance
Refers to a day an employee is scheduled to work or actually goes to work, often contrasted with days off.
明日は出勤日なので早く寝ます。
Tomorrow is a work day, so I'll go to bed early.
今月の出勤日は20日です。
There are 20 work days this month.
出勤 is the act of going to work, while 出勤日 specifies the day itself.
Compound of 出勤 (attendance at work) and 日 (day).