The phrase "graduate on time" means completing your studies and receiving a degree within the expected or planned duration, without any delays or extensions. Full definition
According to 2010 graduation rates, 51 % of city school students graduated on time. (wxxinews.org)
A third of the district's seniors don't graduate on time, and more than 90 percent of high school students there are not proficient in either language arts or math. (npr.org)
Only 55 percent graduated on time in 2015, although 83 percent made it to a diploma after six years. (hechingerreport.org)