Honestly I think Steve was sharp enough to have immediately left the car upon reading the word "filament". Those extra seconds finishing the note cost him his life.
shareThat's not a plot hole as it doesn't affect the plot.
shareYes, it's not a plot hole and as we see throughout the film, Steve is a little too full of himself and too over-confident. He didn't possess Bishop's sense of caution.🐭
sharePlus, I think the door was rigged to stay locked (you see JMV trying to open the door for a brief second or two just before the explosion....all to no avail)
share
An automatic locking door would certainly work and ensure JMV didn't escape even if he tried to bolt as soon as he saw the note.
The way I would have done it would be to have the 13 second timer activate when the dome light went on just as Arthur set it up, but if the dome light went on twice (like once getting in and then opening the door to escape), it would bypass the timer and detonate immediately. That way would ensure it didn't require adding anything to the car besides the bomb and the timer circuit board.