Heist Lockdown timer inaccurate with increased lockdown time mods

Just did a heist and the lockdown timer got down to 2 seconds and then the box locked early. It appears that the "6% increased time before lockdown" on my disguise kit and hooded cloak is increasing the timer display value, but not actually increasing the time, so the extra 12% nets me 2 more seconds, starting the timer at 22, but really I'm still only getting 20 seconds to grab the item.