Factual error: When George starts time traveling in his lab, we see the sun and moon cross his field of view. But then we see stars circling Polaris in the same area. Polaris is nowhere near the path of the sun.
Factual error: In 1917, James Filby has driven and parked in the wrong direction in front of Filby's Department Store. (00:33:08)
Answer: Earlier in the movie, Mrs. Watchit hands an envelope to Philby with a note inside to inform everyone that if George doesn't show up at 8:00, then they can start dinner without him. This is what he most likely left on the mantle before he started his journey through time.