When Mr Fraley sees Mac working late he asks what he's doing there at almost midnight. Moments later Tony gets caught at the school and him and Mac head to the construction site. The security guard asks what he's doing at the site at 3am. Mac and Tony return to the school, the clock in the darkroom shows 4am. Why did it take 3 hrs to get to the site and less than an hour to return?
It would take more than two or three pumps on the spray-bottle's handle to purge the "original" liquid from the intake-tube and draw up the "new" glycerol/water mixture that was now in the bottle.
(at around 1 min) When the security guard asks Mr. Fraley about him working late, the boom mic can bee seen above the guard's head.