Explain this, cause it's not make any sense for me..

Rating: 6/10 (2 December 2016)

This is a big major fatal failure for the script : Factor "x" was causing the differences time for humans infected after they got bite from zombies or what??
For example how can one got bite and instantly infected while others not.. I mean, come onnnn... They still fully conscious after got bitin... And whooppss... One of the support character even can hold the door for maybe 2 or 3 minutes with all of his strength after got bitin and show no infection symptoms instantly? Not mention the main antagonist character may open the door while his eyes was into zombie eyes???? And... Last but not least....... The main protagonist character even can have a little talk with his daughter, took her to the machinist cabin, and give her a daddy final advise also can memorize something ?.. How can the director and the scriptwriter explain this??.. The cheerleader girl got bite at her legs, and it not took long for her to transform into zombie and bite her friend?????... Hey... I almost forget to mention for the first bite scene instantly transform the train staff in her blue uniform into zombie too!! And... and... The baseball team, who is far younger and I think is fitter in healthy than the main protagonist character also transform instantly after got bitin at the station.. This is one of a crap movie... ...Huhh...