By default, all users can enter time to all active projects provided you have the relevant subscription package and security permissions. There are only a few things that would prevent you from doing this:
- Employee Control has been implemented and that project is not assigned to you.
- Project Assignments have been implemented and you are not assigned to that project.
- The 'Prevent time entries' rule has been applied to that project. In this case, no one can enter time to the project.