You can create invoices for billable hours in Xero for free by utilizing a free time tracker that offers integration with Xero. Here are the general steps to follow:
Create a free account on Jibble.
Set up activities, projects, or clients (if required).
Invite employees to your Jibble organization.
Integrate Jibble with Xero.
Start tracking worked hours in Jibble via mobile, desktop, or tablet.
Once finished with a task, send invoices directly to a contact in Xero from your time reports in Jibble.