Fourth meal is paying off for fast-food chains.

McDonald's reports the fastest-growing time is early morning/late night. The company reported profits up 11 percent in the previous quarter, and they are thanking late-night eaters for that.

More restaurants are opening 24 hours. One-fifth of the workforce now works evenings, causing disruptions in typical eating schedules. Early risers are passing late diners in restaurants.

College students, workers picking up late shifts and early-rising elderly all have more choices than before with Burger King and Dunkin Donuts chains adding more hours.

Late-night dining may be boosting McDonald's bottom line for now, but a recent rise in the price of beef means the prices will trickle down to the consumer soon.

Read More:

• Late-Night Sales on a Roll For U.S. Fast-Food Joints (Wall Street Journal)
• McDonald's profit climbs 11% in 4Q (Chicago Tribune)