hen entering time Zoho People does not enforce the default "Billable" or "Non-Billable" status for a job if the "Billable Status" setting under Time Entry > Settings > General Settings > Time Log Field Customization is not checked.

For example: 

If this setting is not checked:

Screen shot showing the job is set to "Non-Billable"

This screen shows that time has been entered to this job. 

If I edit that same time entry and change it to a Billable job the time entry remains "Non-Billable".

In this screenshot you can see that this job is Billable.

The timesheet now shows it as Non Billable: