Plot hole: We see Michael wearing the mask throughout the day, from morning at the Myers House, to mid-day outside Laurie's school, to afternoon when Tommy is leaving school, yet when Laurie and Annie see the sheriff in front of the hardware store on the way to their babysitting jobs (presumably in late afternoon or early evening), the store's alarm is still ringing and the sheriff mentions that one of the items stolen was a Halloween mask.
Plot hole: According to the denouement sequence shown in the film, Linnet Ridgeway is shot asleep in her bed approximately three minutes after retreating from the lounge. Less than 2.5 minutes pass from the moment Linnet leaves the lounge to the moment when Doyle is left alone by the other guests. It takes another 30 to 45 seconds for him to pick up the pistol, rush into his cabin and kill his sleeping wife. How could Linnet have walked to her cabin, taken off her jewelry, changed into her night-dress, retired to bed, and fallen asleep in 180 seconds? (00:59:00)
Suggested correction: The sequence never showed when Linnet goes to sleep. We can't be sure how long it is between her leaving and Simon shooting. All we know is in the actual scene she leaves after having already taken a sleeping pill. This is "movie time", not real time. 3 mins can be 30 mins in movie time. The flashback sequence doesn't clarify anything based on her timeline.
This...is not at all what happens. This is the 1978 movie; Linnet is playing cards with the others up until a moment before cutting the game short not by her choice but because of Jackie's interference, so certainly took no pill in advance nor does she take one on screen, and the characters interact with no interruption from that point on leaving no room for an implied 'movie time' elapsing at a significantly slower rate than 'real' time.
Plot hole: At the Jefferson Institute, to evade the security guards, Dr. Wheeler climbs into the space above the ceiling, crawls over the air ducts, then onto a catwalk, and finally escapes lying atop an ambulance heading to the airport, then immediately goes to the hospital to warn Dr. Harris. Throughout this entire ordeal she never gets disheveled, nor does her white doctor's uniform ever get dirty or wrinkled. She is perfectly clean and groomed.