Unable to trigger OTL Fast Formula to get hours for employees who does not have time card entry

Summary:

We are not able to return the hours from published schedule through fast formula when there is no time entry.

Content (please ensure you mask any confidential information):

We are trying to get on call hours flag and start and end time from the published schedule. During this time employee will not have any time entry or punch time in the Time Card.

We need to write certain logic based on the on-call hours.

But the challenges we are facing here is, if the employee has no time entry for the day with On call shift, we are not able to return the on-call hours from published scheduled. Ff is not triggering only.