How long after an employee pays $10 out of pocket, should he ask about the status of his reimbursement ?

Let’s say he was sent an e-mail asking if he has a ten-dollar bill, as the requester needs that amount to be mailed to client’s residence.  Obviously, the requester is unable to do this herself, since she’s working from home, as well as 99% of the staff, including accounting department.  Therefore, the employee who was in the office that day, mailed his ten dollars to client along with letter that was e-mailed to employee to seal in envelope with $10.  After how much time should he ask about his $10 if he has not yet been paid back?