Why AT&T announced the Time Warner deal on a Saturday

While investors were away enjoying their Saturday nights, AT&T announced a $85-billion deal to buy Time Warner.

If the weekend announcement seems like unusual timing, it's because it is. Less than 3 percent of all mergers worth $100 million or more over the last decade were announced over the weekend, and most of those announcement were on Sundays, according to a CNBC analysis.

Of course, the most popular day for announcements traditionally is "Merger Monday," which gives companies a full week of media and investor attention to capitalize on the news. But the incentives seem to be different for the largest mergers like AT&T/Time Warner deal, which are more likely to face media pushback and regulator scrutiny. Those big deals are more likely than smaller mergers to be announced on weekends.

Out of the 20 largest attempted mergers announced over the last decade, six have been announced over the weekend. Two others were announced on Fridays, another relatively unpopular day. Big mergers worth over $10 billion are four times more likely to be announced on a weekend, according to the data.

There is some precedent for AT&T, which announced its $49 billion takeover of DirectTV on a Sunday in 2014 and its $39 billion acquisition of T-Mobile (which was eventually cancelled) on a Sunday in 2011. The pending merger between health care companies Anthem and Cigna was also announced on a Saturday last summer.

AT&T CEO Randall Stephenson told CNBC that the announcement timing was motivated by concerns that the news could be leaked if the company waited. News that the two media companies were nearing a deal broke Friday evening.

Republican presidential nominee Donald Trump came out against the proposed deal on Saturday, saying that if he won his administration would not approve it. Democratic nominee Hillary Clinton said the deal should be closely scrutinized by regulators.

Both Time Warner and AT&T stock prices were down from Friday's close on Monday afternoon, and Time Warner was still trading far below AT&T's offer price of $107.50 per share on concerns that regulators would not approve the deal.