Wiktionary
on the dot
adv. (context idiomatic English) exactly; precisely, especially of a numerical quantity
WordNet
on the dot
adv. just as it should be; "`Precisely, my lord,' he said" [syn: precisely, exactly, on the nose, on the button]
Usage examples of "on the dot".
He powered up the maximum-gain telescopic camera and trained it on the dot of light that was Lucifer.
He strolled up and down for five minutes, then, on the dot of ten, dropped the fat envelope through the letter slot of the apartment house.
If one looks at a black rectangle containing a white dot and a white cross and focuses, let us say, on the dot, he will be able to locate a certain distance at which the cross disappears.