In Highschool of the Dead, how long does it take for a person to become one of 'them' (a zombie)?
It's most reasonable to suspect the severity of the bite.

When Hisashi was attacked, he had a layer of clothing protecting him. So it's safe to say that the bite didn't get very deep penetration. Hence why he was able to last the entire episode (several hours)?



Oh the other hand, Tejima-sensei from earlier in the first episode took a large bite directly on his naked arm. He was zombified almost instantly (under 1 minute).