It actually was 5 minutes, near the end if the fight King Kai says Gokys five minutes are nearly up and in the anime Frieza in the semi final says he held back too much and he'd give the planet another 2 minutes at the most.
Between King Kai confirming 90% if the fight took place in under 5 minutes and Frieza saying he's gonna give it another two but was beaten shortly after we can confirm that namek going kasploosh was with 7 minutes with the latter two being mostly goku trying tyo find an escape.
