I work in the Federal Government, and this isn't true. You have alternative work schedules (4/10s, 5/4/9, maxiflex, etc.) but you're still going to work 80 hours unless you take leave. You gain annual leave every pay period and the amount is dependent on how long your federal service has been. But when you start (1-3 years) you only get 4 hours per pay period.
Maybe you're seeing people who have long federal service (15 years) that gain 8 hours/pay period use their leave. That's their choice but they're still working 40 hours on paper regardless.
Might want to scan your computer for spyware. I used to have that issue a long long time ago.