The scheduler developed a 5 day, 10 hr per day calendar for one of my projects yet developed budgeted labor units as 8 hrs per day, 5 days per week.

Example; Activity OD RD Budgeted Labor Units Remaining Labor Units
Perform 20hrs 20 hrs 15 hrs 15 hrs

When I questioned this, the response was that in schedule space you don't receive 100% productivity for duration, duration hrs is one thing and budgeted hrs to perform work is another.
So my question is; If he is correct how can you have more time in the schedule to perform work than what you have budgeted?