Suzanne: You're not gonna believe this, but Dex is here.
Maddie: What is this? The night of the ex's? Colin's here, too.
Suzanne: Where?
Maddie: Right there.
Suzanne: You know, I can sort of understand the whole bad boy thing, but what did you ever see in him?
Maddie: Oh, codependency, the whole Mother Teresa complex, believing I could change someone into something else, thinking that great love and great drama were the same thing, insecurity... Oh, and the guy can fuck.
Jason: She stuck a lipstick in her boob and it fell out of her pussy... Okay?
Jason: No costume, no candy motherfucker.
Answer: It took Maddie several minutes to climb down to the basement after Colin fell through the floorboards. Those couple of minutes was all the time needed to infect him.
Again, he wasn't bitten or kissed, so he shouldn't have been infected.
That's why he states it took her a good amount of time, as the viewers don't know what may have happened... Plus, technically, he was humped.