There are other hidden merits with this system. If a leader has to approve all of his subordinates' reimbursement applications together at once he/she probably won't look through them carefully. But if they come in a timely fashion, the leader can look through each one and, when necessary, offer a little disciplinary advice regarding excessive use or even suspend use when an employee reaches that month's budget. Oh, how the accounting department will be elated.
That said.... the accounting people will still want to reimburse employees only once a month. This means you want a workflow in which reimbursement applications/approvals can be done anytime during the month, but the actual reimbursement happens once a month.
(One process a month for each employee. In order to be able to apply/approve at any time, employees/leaders need to always have at least one split token at hand. These definitions differ according to the workflow engine.)
During the month, the process only moves from [3. Approve] to [4. Calculate Reimbursement Fee] when the employee selects "OK to finalize" in [2. Add Expenses for Reimbursement]. Not bad.