Taco Bell has been the king of late-night fast food for years, selling diners on its fourthmeal nachos and tacos in the hours between dinner and breakfast.

The chain's rivals have taken notice, and they aren't as willing to cede the late-night hours anymore. McDonald's (MCD), Burger King (BKW) and others are stepping up their extended-dining options. And while they aren't advertising for the wee hours the way Taco Bell is, it's clear they hope to take a bite out of the fourthmeal strategy.

In the Tampa Bay area, for example, McDonald's has been aggressively expanding its 24-hour service. Now more than 70% of the 186 restaurants there are open 24 hours, the Tampa Bay Times reports. Nationally, about 40% of McDonald's restaurants never close.

McDonald's says the restaurants open 24 hours see about a 10% uptick in sales, writes the Times' Susan Thurston. One franchise owner told Thurston that never closing eliminates the expenses associated with shutting down the restaurant and then firing up the equipment again in the morning.

Taco Bell, owned by Yum Brands (YUM), says it decided to emphasize its fourthmeal because Americans are eating later than in the past. Nearly 45% of Taco Bell's key demographic -- males ages 18 to 29 -- eat later than 7 p.m. Taco Bell also found in 2006 that about 40% of Americans work a nontraditional schedule, meaning they put in hours late at night and on weekends or work extra-long shifts.

Burger King requires its restaurants to stay open until 11 p.m. or midnight, depending on the day of the week, but now several hundred are open 24 hours, The Wall Street Journal reports. A third of Dunkin' Donuts locations are open 24 hours as well. About a fifth of all employed Americans work in the evening, one sociology professor told the Journal.

"I think we really have moved to a clockless day," John Costello, the marketing chief for Dunkin' Brands (DNKN), told the Journal. "People are working longer hours, in many cases multiple jobs, and are more time-starved than ever before and they want the flexibility to have a full variety of products that aren't limited by time of day."

More from Top Stocks

• Comcast's NBC could profit from Olympics
• Is market being irrational about Facebook?
• What a good stock looks like