The 24-year-old, who gave birth to Lucas Cruz Comrie on March 20, confessed that time has flown by since she welcomed her son.
"I love changing diapers!" Duff told People. "I'm really good at it. I've got it down."
"There are so many fantastic things [about motherhood]," she continued. "Everything's been really wonderful, and the time's just been flying by. I want it to slow down."
Duff recently admitted that she was surprised by the lack of sleep she's been getting since becoming a parent.