To set a custom environment variable for a single workflow, you can define it using the env key in the workflow file.
Example:
env:
DAY_OF_WEEK: Monday
Note: The scope of a custom variable set by this method is limited to the element in which it is defined. You can define variables that are scoped for:
The entire workflow, by using env at the top level of the workflow file.
The contents of a job within a workflow, by using jobs.<job_id>.env.
A specific step within a job, by using jobs.<job_id>.steps[*].env.
Reference:
https://docs.github.com/en/actions/how-tos/write-workflows/choose-what-workflows-do/use- variables

Example:
on:
schedule:
- cron: '30 5 * * 1,3'
- cron: '30 5,17 * * 2,4'
Reference:
https://docs.github.com/actions/reference/workflow-syntax-for-github-actions

[B] You can use self-hosted runner to run more than 6 hours job.
Self-hosted runners give you the opportunity to persist whatever you like for your jobs and not be subject to the six-hour time-out in hosted virtual environments.
[C] Give you more control of hardware, operating system, and software tools than GitHub-hosted runners provide.
All runners can run Linux, Windows, or macOS.
Reference:
https://github.com/orgs/community/discussions/26679
https://docs.github.com/en/enterprise-cloud@latest/admin/managing-github-actions-for-your- enterprise/getting-started-with-github-actions-for-your-enterprise/getting-started-with-self-hosted- runners-for-your-enterprise
https://docs.github.com/en/enterprise-cloud@latest/actions/concepts/runners/self-hosted-runners

The correct options are JavaScript entry file such as main.js or index.js, Action metadata file action.yml or action.yaml, and Container action Dockerfile.
The Action metadata file action.yml or action.yaml is mandatory because it declares inputs and outputs and it instructs GitHub how to run the action. Both JavaScript and container actions rely on this metadata to execute correctly.
For a JavaScript action the JavaScript entry file such as main.js or index.js is the script that the runner executes as directed by the metadata. GitHub expects a committed distributable script, so the entry file must be present in the repository.
For a container action the Container action Dockerfile defines how to build the image and what command to run, which makes the Dockerfile required for the action to work.