There is no restriction on the number of admin users. If an admin user does not create timesheets or expenses, then you are not billed for their usage.
To grant an employee 'admin' level access to TimeRewards
- Go to Employee list
- Select the Employee to whom you want to give admin access.
- Under General tab, change the Role of employee to Employee Admin.
You can also customize access to TimeRewards by creating Roles under Setup | Role Preferences, and granting each role specific access to TimeRewards features.