Employees are history-keeping: department, job title and employment status are versioned, so a timesheet from March is read against the department the person belonged to in March. Two boundaries are worth knowing. First, the analytics carry what is needed to slice time — code, name, department, title, status — and nothing more: contact details and bank fields never enter the analytics at all. Second, a time entry wears its employee's department, because entries carry no department of their own.
Projects show current values: code, name, status, billing type — time-and-materials, fixed-price or non-billable — and, importantly, the project's customer. Every project belongs to a customer, so time can always be read by the client it was worked for.