Explanation
To perform multi-staged jobs, where the second job can only begin after completion of the first job, two service appointments can be created and linked by setting the Related Service Appointment field on the second service appointment to point to the first one, and setting the Time Dependency field to After Previous.
Creating one service appointment with the total duration of the two jobs and assigning two resources would not ensure that the second job starts after the first one. Creating two service appointments and scheduling them to the same resource or creating one service appointment and scheduling it to two different resources would not create a dependency between the jobs. References:
https://help.salesforce.com/s/articleView?id=sf.fs_service_appointments.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.fs_service_appointment_dependencies.htm&type=5