during working hours; on company time
Refers to the period when one is officially at work; often used in rules or descriptions of work-related activities.
Please refrain from personal calls during working hours.
You need permission to leave the office during working hours.
Similar meaning, but 勤務時間中 is more common in some contexts; 就業時間中 is slightly more formal and often used in company regulations.
Compound of 就業 (work, employment), 時間 (time, hours), and 中 (during).