When I tried to develop custom job; I spent couple of days without much success. But eventually was able to do with the help of some posting queries, SAP document. But in 7.3, it is bit different. I am posting detailed steps that need to be followed for custom task development and scheduling the same.
1) 1) Create EJB Project

1) 2) Create Scheduler Job


3) 3) After creating Scheduler Job, project structure will look like:

1) 4) Only change needed in configuration file: Add following line in ejb-j2ee-engine.xml next to </ejb-name> tag
<jndi-name>TestJob</jndi-name>
2)
5) Code for scheduled job in onJob() method. Deploy EJB.
3) 6) Login to NWA. Search for Job Scheduler in NWA

1) 7) Go to job scheduler; which will take you to

1)
We will be able to locate the Custom deployed task in NWAS-Java scheduler 
1) 9) Creation of task referring to custom job created
:
10) Click on Add button and we can select TestJob created


11) If there are any parameters of the job, configure them

12) Types of scheduling:Recurring, Recon, Simple;

We are done with all the steps to be followed for creating and scheduling custom job.