Yes. You can set the default invoice template to Hourly for all your projects irrespective of their contract types at the global level (Global Settings > Template Assignments). However, it is recommended that you use the templates in accordance with the contract types of the projects as the template design focuses on the contract types and the invoices may be missing some information if you do not use the recommended templates. This is why the invoice templates are mostly categorized by the contract types. You can also set the invoice template at the project level. Check the Core Help for details on assigning invoice templates at the project level and global level.