Business hours are used to specify the days and hours when your company's employees work. You can create multiple sets of business hours for different time zones or regions and assign them to users based on their location or function. To meet the requirement of having different business hours for reps on pacific time and eastern time, you need to create one set of business hours per time zone and assign them accordingly.
References: https://help.salesforce.com/s/articleView?id=sf.customize_supporthours.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customize_supporthours_assign.htm&type=5

The login history is a tool that allows administrators and users to view information about recent login attempts, such as date, time, status, source IP address, browser type, platform, application, and login type.
Administrators can use this tool to identify why a user is unable to login to Salesforce by checking for any failed login attempts and their corresponding error messages or reasons. References:
https://help.salesforce.com/s/articleView?id=sf.monitoring_login_history.htm&type=5

To free up user licenses for new users, the administrator should deactivate the former employees user record.
This will prevent them from logging in and using Salesforce resources, but preserve their historical activities and data. Deleting or freezing user records will not release user licenses. References:
https://help.salesforce.com/s/articleView?id=sf.admin_usermgmt_licensing.htm&type=5

To update the shipping address on selected orders associated with an account when the shipping address is changed on the account, the administrator should create a screen flow on the account page that lets the reps choose which orders they want to update with the new address. This will give them more control and flexibility over which orders are affected by the change. An autolaunched flow on either object will not allow reps to select specific orders, and may cause unwanted updates or errors. A screen flow on the order page will not be able to update multiple orders at once. References:
https://help.salesforce.com/s/articleView?id=sf.flow_build_screen.htm&type=5

Flow Builder is a tool that can be used to create an automated way to delete records based on field values.
Flow Builder can create flows that define the logic and actions for deleting records, such as finding records that match certain criteria and deleting them in bulk. Flows can be scheduled to run at regular intervals or triggered by other events or processes. References:
https://help.salesforce.com/s/articleView?id=sf.flow_builder.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_concepts_delete.htm&type=5