how to print user name on print invoice
create a custom field with users as drop-down list.
how to print time in invoice?
any data other than those available as default in Manager to be shown on the document can be created as a custom field.
I agree with your suggestions though but for security reasons I think the are few things that manager should be able to handle to remove the human involvements. Personnel with bad intentions will always take advantage of any little opportunity. I think it will be right if manager can automatically print user name and time on documents such as invoice, receipt and payment, etc. forms.