The $500 勤工 can be an optional bonus.
Is your husband receiving the 底薪 only? Your husband should ask his manager to seek clarification of the meaning of optional punctuality bonus.
It seems that the Company use the optional terms to protect itself if in case the business is no good, they have the authority to cancel this punctuality bonus or change the critiera for achiving this payment.
Thus, your husband'salary package should be as follows: