Timed play
Timed tournaments use a clock or timer to determine the length of each half of a game. At present, NAQT is the only question provider whose rules call for timed halves - 9-minute halves for high school games; 10-minute halves for college.
History
Reflecting the evolution of quizbowl away from College Bowl, the formerly nigh-standard practice of running games on a clock is now nearly extinct at the college level. In the early 1990s, only the most purist ACF events, such as the Georgia Tech MLK and ACF Nationals, were untimed. By the turn of the millenium, the only timed tournaments remaining were NAQT Sectionals and ICT, Stanford's Cardinal Classic, Michigan MLK, and Penn Bowl, plus of course all College Bowl-run events. Cardinal Classic dropped the clock starting in 2001, Penn Bowl in 2003, and MLK in 2006. In order to better simulate the ICT environment, the 2008 and 2009 FICHTE tournaments used the clock and NAQT's 2-second recognition rule.
Today
Now, only the NAQT SCT and ICT are timed among college quizbowl tournaments. Teams earn a discount by bringing a clock to their Sectional site. NAQT's timing rules allow for somewhat more sanity than College Bowl's used to, but are still open to games ending with a poor moderator reading 18 or fewer tossups.
At the high school level, despite the official NAQT rules' call for 9-minute timed halves, most tournaments using IS-sets run untimed 20/20 rounds, which NAQT allows. The HSNCT continues to use the clock, but many top competitors play no other tournaments on the clock during the entire competition year.