Continuity mistake: When the time traveler is first starting to travel in time, the sun moves across the window from left to right, indicating that the window faces south. When night arrives, however, the view is of the stars moving right to left, indicating that the window is facing north.
Continuity mistake: At the very end of the movie, when Mr. Wells' housekeeper bids Mr. Filby goodnight, watch how quickly the upstairs lights get turned off after the downstairs lights. Considering that the time traveller was gone and she was the only one left in the house, that old woman must have RUN up those stairs faster than any human being could...
Continuity mistake: When George stops his time machine at 802701 A.D. he stops it too fast and falls out of his time machine. While he's lying on the ground rain falls out of the sky and only lands on him and a little bit of the ground. When George stands up however his hair and his clothes are completely dry and steam is rising from the ground.
Continuity mistake: When George stops in 1917 he kicks some planks from a fence that has 4 small signs and a plank missing, in the next shot 3 signs are gone and the missing plank is reattached. After he talks with Filby Jr. he climbs back through the original fence (the one with the missing plank and 4 small signs, plus 3 other ones that were out of sight in the first shot).
Continuity mistake: When the Time Traveller gets back into the machine after the volcano scene, because the numbers are turning so fast, you can only see the first number; the first time you see this, the first number says 8, then 9, indicating 8,000 then 9,000 years, then it cuts to the Traveller for a second, and when it is seen again, it says 8,000 then 9,000 then 10,000.