What are "Packages of Services"?
You can read more about the Packages feature here: https://wpamelia.com/packages/.
It allows you to create a package that will include one or more services and appointments for those services. So, with the Basic license, you'd be able to create services and sell appointments one by one. The Packages feature (which is included only in Pro and Developer license plans) allows you to create a Package for (for example) one service, and 10 appointments within that package.
The duration you set is for the package while the appointments within a package are defined by the "Period available for booking" in Amelia's General Settings or individual settings of a service. So, if you sell a package with 10 appointments, and set the duration of the package to be 1 year, your customers will have 1 year to book those 10 appointments.
However, the appointments within a package can be booked as far ahead as you configured the "Period available for booking in advance" in Amelia's General Settings, or individual service setting. For example, if this is set to 30 days, at the time when an appointment is being booked, the customers will be able to choose the dates 30 days from TODAY. Defining the duration of the package doesn't define the availability of appointments.
Please note: The Packages Feature is only available for Pro and Developer license plans.