Adding time to invoices

Hello, i would need to add the time field to invoices. In my country it is mandatory to have time of creation on the invoice. Can i add a custom field or for example change the "due date" to time?

Ok - I have "bodged" something: through the localization file i just changed the due date translation to time and i can enter the time manually. I know it is not ideal but i don't have the time to customize it properly right now...