<P> On September 18, 2006, Time Warner and CBS Corporation shut down The WB and UPN to launch a "merger" of those networks, The CW; meanwhile, two weeks earlier on September 5, News Corporation created MyNetworkTV, originally intended to replace UPN programming on Fox - owned stations that were affiliated with the latter network . </P> <P> The CW broadcasts ten hours a week of programming in prime time, all airing only on Monday through Fridays (the network maintained a three - hour evening lineup on Sundays from 2006 to 2009, when that time was turned over to its affiliates), and five hours on Saturday mornings (its children's program block may bleed into the afternoon hours on weekends on a few stations due to other locally scheduled programs). The CW is the only major network that operates a fully programmed alternate feed for smaller markets, The CW Plus (a successor to The WB's group of cable - only affiliates, The WB 100 + Station Group, which launched in September 1998 to provide the network's programming to markets where it would otherwise not be able to gain adequate over-the - air coverage), which, as a cost - effective method that reduces programming responsibilities on prospective affiliate stations, fills airtime not occupied by CW network programming with syndicated programs and infomercials; The CW Plus is distributed via digital subchannel and cable - only affiliates, making it also one of the only networks that has local affiliates that do not broadcast over-the - air . </P> <P> MyNetworkTV originally started as a conventional network with a format primarily consisting of English language telenovelas; however, after experiencing continued low ratings for its prime time - exclusive schedule (even after several programming revamps that followed over the next three years after the initial format faltered), it converted into a "broadcast syndication service" in September 2009, adopting a format made up of reruns of series originally aired on other networks for ten hours a week on Monday through Fridays . Ion broadcasts 24 hours a day, seven days a week (though only eighteen hours of its schedule each day consist of entertainment programming, with infomercials and religious programming making up the remainder of the schedule), making the Ion network the largest English - language commercial television network to be totally responsible for its affiliates' programming . Ion differs from other commercial networks in that the majority of its stations are owned - and - operated by its parent company with very few affiliates, and it is distributed exclusively via cable and satellite in markets where the network does not have a local station; Ion was the last of the seven conventional English language commercial broadcast networks to expand into distribution via digital multicasting, having relied entirely on cable and satellite distribution in markets where it otherwise could not maintain a primary affiliation until 2014, when it began accepting subchannel - only affiliates through deals with Telemundo Station Group and Media General . </P> <P> With the digital television transition, which was completed in two phases in February and June 2009, the use of digital multicasting has given breed to various networks created for distribution on these multiplexed feeds of new and existing stations . However, for the most part, very few of these networks have been able to gain a national reach on parity with many of the conventional commercial and non-commercial networks, in part due to the fact that many stations transmit high definition programming on their main feed in 1080i, which requires a bitrate less compartmentalized for allowing more than one multicast feed (which are generally transmitted in standard definition) without risking diminished picture quality; some alternately transmit their main feed in 720p, which favors multiplexing of more than two subchannels at a time (ATSC 3.0, which began development around the time of the 2009 transition with FCC consideration to replace the current ATSC 1.0 as the technological standard for digital television expected to occur in 2016, utilizes improved compression technology able to fit additional subchannels on a single programming stream as well as allowing for the transmission of high definition content in the 4K resolution format). </P>

When did television started broadcasting 24 hours a day