The break before the start of overtime is shown as a brief intermission with the teams on the benches, which is correct for the regular NHL season. However, in a tied playoff game, the teams head to their locker rooms for a normal length intermission. The Penguins probably would have noticed that their locker room had been riddled with bullets and the bodies of a few bad guys on the floor.
In the last minute of any period the clock shows tenths of seconds. In the last period of the game in the movie in one shot it shows the clock correctly, then in the next it doesn't show the tenths of seconds.
When Carla takes Emily into the kitchen and kills the Secret Service man she shoots him in the head with a Sig Sauer P226 9mm, but in the elevator she shoots him two more times and tries to shoot Emily with a Heckler & Koch VP70 9mm.
During the fight in the kitchen there is food cooking (staff would not leave so many stations still cooking for one person to clean up) and none of the food on the grill or deep frying is burnt despite the considerable time elapse.
A helicopter's lift is always in a direction nearly parallel to the rotor axis, so it cannot come close to maintaining a position where its nose is straight up. In such a position it would move violently sideways (the rotor leading) and fall rapidly.
Many items in the kitchen are up and running after all the cooks and chefs had left for the night. This is because Andy, who was charged with cleaning up after everyone as stated by someone, was dead, and therefore the kitchen would still be running.
The Stanley Cup Finals are in early to mid June so there is no way the Civic Center's retractable roof would have been open at that time of year during a hockey game. It would have raised the temperature of the ice and made it soft.
It must have taken Foss and his associates a lot of planning and organizing to pull this off. So why would they plan to carry this out in the seventh game, when there's every chance the seventh game won't be required?
Although it can be seen as a plot hole that one of the henchmen can see from long distance that its McCord and not Tulliver that is on the ice, while the team mates can not, the henchman just saw the real Tulliver sleeping in the locker room and therefore is naturally suspicious.