It was a month into the fall TV season last week, and we only just started getting the first indications over the fate of new broadcast series. That's not because this year's freshman slate is handing advertisers record audiences; they're often improving on the time slots they took over, but they're not matching the ratings networks would have demanded in the old days.

Instead, broadcasters are showing new patience as more TV viewing takes place days after initial airings and across a variety of devices. That's requiring them to evaluate the success of their series in a new light: a plethora of data that can take days or even weeks to marshal and even then requires interpretation that's not always straightforward.

"It used to be that you got overnights in the morning and nationals at 1 p.m. and then some weekly info," said Kelly Kahl, senior VP-Primetime at CBS. "Now there are four to five data sets a day. It's hard to keep up with all of it."

Marketers are, for the most part, happy to wait and eager to look at metrics beyond traditional ratings—just as long as they aren't stuck running commercials in a flop that stays on the air too long.

"We don't want networks to keep a show going, even if it does receive a lift from delayed viewing, if ratings keep falling, because it becomes a problem for reach frequency," one media buyer said. "Then what happens is we have to look for different sources to make up for the supply, and that won't necessarily be in TV."

Networks were once so quick on the draw that one episode could doom a show. NBC's 2008 series "Quarterlife," originally a web series about 20-somethings that the network picked up for traditional TV, never got a second episode on the air.

Instead of making snap judgments, executives are now practicing patience, hoping to allow new shows to develop an audience and perhaps reveal some gems that could be lucrative down the road in distribution deals. This strategy involves a delicate dance of balancing future revenue opportunities against an immediate present in which advertisers demand reach.

The continuing decline of TV ratings leaves a dearth of gross ratings points, most of which marketers can't make up on digital or streaming platforms like Netflix, and it is still the job of networks to find the next "Empire."

"That's the crux of the issue: How do we balance long-term revenue opportunities with the right now?" said Andrew Kubitz, head of scheduling at ABC. "If we love the creative of a show, we are more willing to bet on the long-term revenue."

Even as network executives downplay the importance of generally downward-trending live-plus-same-day viewing, it remains part of the decision-making process. "Primary live-plus-same-day numbers are an indicator of what the C3 rating will look like," Mr. Kubitz said.

"Live-plus-same-day ratings still provide a snapshot of how a show is performing compared with the competition," said Jeff Bader, president–programming planning, strategy and research, NBC Entertainment.

Executives look next to Nielsen's live-plus-three program ratings, which can take five days to arrive, and commercial ratings for the three days following a show's airing, or C3. That's the metric that means everything to marketers, but it takes up to three weeks to receive.

To decide the fate of a series, however, network executives are also increasingly mining data drawn from video-on-demand and streaming viewing, plus social buzz and the potential to make money by selling a series into syndication or streaming platforms.

While networks have a loose rubric of the metrics they look at and how much weight they put on each, the methodology varies not only from channel to channel but from show to show.

Take Fox's highly anticipated "Scream Queens." The Ryan Murphy horror-comedy premiered to just 4 million viewers, which was certainly a disappointment. But that audience grew 83% to 7.3 million in three days of viewing, including Nielsen's live-plus-three ratings and streams on Hulu and the Fox Now app.

It helps that "Scream Queens" is also produced by Fox, meaning there's the potential for incremental revenue from distribution deals, and it also attracts a young female audience that advertisers are having trouble reaching elsewhere.

David Madden, president-entertainment at Fox Broadcasting, acknowledged that he would love to have several versions of "Empire" on the schedule, but said different shows work in different ways.

Sunday nights may not attract an especially large audience for Fox, for example, but it is skewed heavily toward young males, a group that's a challenge to get through TV.

So Fox is evaluating its series by studying how viewers are prioritizing them. This does not mean they have to watch it live, Mr. Madden said; the goal is to see if there's a reliable long tail. He points to "Last Man on Earth" as an example. The series premiered last season to 4.1 million viewers, jumped to 6.5 million in the seven days following and was up to 11.9 million 30 days after the premiere. Those aren't the commercial ratings that marketers watch, but they suggest there's an audience for further distribution at a minimum.

"We have been trying to be as patient as we can," Mr. Madden said, noting that Fox is spending more time analyzing 30-day multiplatform data.

"As an old-school scheduler, one of the most important things to me is week-to-week trending," said CBS's Mr. Kahl. "If you are seeing growth in delayed viewing week to week it suggests word-of-mouth is starting to grow."

CBS's new drama "Limitless," based on the 2011 movie about a drug that bestows heightened intelligence, premiered to a 1.9 rating among 18-to-49-year-olds, which Mr. Kahl called "a good number," but not indicative of a smash hit. Then the show added over 3 million total viewers in the three days that followed, and its rating jumped to 2.9. The following week, the 18-to-49 rating held even with the premiere. "When you have a show that matches its premiere rating, that then looks like a great number," Mr. Kahl said.

"Limitless" received a full-season order late last week and "Code Black" got an additional six episodes. Elsewhere, NBC's "The Player" was cut to nine episodes, while ABC reduced its order of "Blood and Oil" to 10 episodes.

Digital viewing plays less of a role in CBS's analysis since it has been notoriously harder to measure, and social buzz is "the flimsiest of all the numbers," Mr. Kahl said. "If no one is watching it doesn't matter."

"We are not at a place where we would make a decision if a show is tanking on linear [TV] but has huge digital ratings to keep it on," NBC's Mr. Bader said.

ABC's Mr. Kubitz said the calculus has broadened beyond what will accumulate the most commercial ratings to encompass what will generate the most revenue.

The appeal of distribution on platforms like Amazon and Netflix depends in part on whether the broadcasters get a cut, which they don't if they didn't make the show.

"It's important for networks to have a stake in the game by owning the content outright or a piece of it," said Chris McCumber, president, USA Network, whose drama "Mr. Robot" has become somewhat of a model in this new ecosystem.

USA renewed the psychological thriller, which stars Christian Slater as a hacker leader, for a second season before the first episode ran on TV. It based its decision on the reception it received in the weeks leading up to its linear debut, when the pilot received nearly 3 million views across video on demand, USA's website and third-party distributors like Facebook.

Less important were the linear ratings, which weren't overly impressive when they arrived. The first season of "Mr. Robot" averaged 1.4 million live-plus-same-day viewers and a 0.5 rating among adults 18-to-49 years old.

USA was right to renew "Mr. Robot" when it did, Mr. McCumber said. Ratings grew 75% in C3; the show delivered 7.6 million video streams during the season; people watched its streams longer than other USA series (15 minutes compared with six minutes); and the series is still generating about 900,000 video-on-demand starts per week.

USA is already grabbing more revenue by selling the series' back episodes to Amazon.