When explaining the Slap Bet, Ted outlines the two previous slaps. However, the slap shown happening at MacLaren's pub is not part of the five, and occurred before Marshall had been awarded five slaps.
When "Marshall" puts the Laptop on the dining table the countdown shows the final hour before the slap. Earlier it has been said that the slap will take time at 3pm. This is not possible if you look at the clock hanging on the wall because it shows 4:20 pm, however the clock always displays 4:20.