A client calls and you'd like to start a project immediately, so no billable minute gets lost? You can do that by using the "Quick start project".
In the configuration you can set, what dialog should open, when you stop the quick start project. This might be: No action at all (This will always create a Quick start project in your project manager you can rename manually), Open action menu when stopping project (see screenshot below), Ask for project name on stop (opens a dialog you can enter the new project in), or you can transfer the project to any chosen client when you stop it.
If you choose the action menu, you'll again get all other options, but the entry of the project name.
After you click on the Quick start button on your timebar, the quick start project starts running:
If you click "Stop", the above mentioned dialog will open and you can decide what to do with your timestamp. Here's a screenshot what a quick star project will look like in your project manager:
Quick start projects are always main projects. If you want it to become a sub project, drag&drop it onto another main project. You can change the name of the project in the project manager by hitting F2 with the mouse focus on the project.