If an event attendee should receive partial hours or credits for an event due to leaving early, arriving late, etc., anyone with Manage Attendance permission has the ability to override an individual attendee's hours or credits.
From the event page:
1: Scroll down to the Event Attendance section to view the list of participants who are registered and/or confirmed in an event.
2: Click the three dots on the far right to open the attendance options.
3: Click Edit Attendance, then click the lock icon to “unlock” and make any of the fields for hours or credits editable.
(For hours, you can use increments like 1.5 which translates to 1 hour and 30 minutes)