How to show time entries on invoices as no charge items?

You can do that by making the time entries non-billable, approving them, and making sure the rule Hide non-billable time entries on invoices is not assigned at the project level. Also make sure that the option Hide non-billable time entries on all invoices in Settings > Billing & Invoices > Invoice Settings is unchecked. See Invoice Settings for details on how this global setting can override the project-level rule. When the rule is disabled at both levels, these time entries then show as 'No charge' items when you create a new invoice for the project from the Invoice Batch screen.