How's that done? By editing the songs so they're about 1/2 to 2/3rds their normal release length.
The format is called Quickhitz and its slogan is "twice the music in half the time." It promises to play 24 song per hour as a result.
Some examples include:
Lorde, “Team,” 1:52 (vs. 3:32)
Clean Bandit, “Never Be,” 2:23 (vs. 3:45)
Magic!, “Don’t Kill The Magic,” 2:13 (vs. 3:39)
Iggy Azalea, “Fancy,” 2:07 (vs. 3:16)
JRDN, “Can’t Choose,” 2:20 (vs. 3:57)
Sam Smith, “Stay With Me,” 2:02 (vs. 2:53)
Marianas Trench, “Pop Music 101,” 2:11 (vs. 4:07)
Zedd. “Clarity,” 2:00 (vs. 3:56)
If you're an artist you can look at this format two ways - If there are more slots on the playlist, there's more chance for new music to find a place, or, "You're messing with my art by editing it."
As for the latter, that might not be a great argument since radio has had specially edited songs for 50 years to fit in the format.
So while you may not hear Quickhitz on one of your local radio tomorrow, the next time you do hear a station that seems to be playing more songs than normal, you know what you're listening to.