(at around 30 mins) Ralph (Rod Taylor) and Jane (Debbie Reynolds) are sitting next to each other in front of the window. In the next moment, Uncle Jack (Barry Fitzgerald) then appears in the room, but now Ralph is sitting at the opposite end of the table away from Jane, and Uncle Jack takes the seat where Ralph had been.
At one point when Tom Hurley is driving his brother-in-law in the cab, Tom takes off his gloves. On the next immediate cut, when Tom stops and sticks his hand out to open the door, the gloves are back on his hands. On the next cut after that, he once again is not wearing the gloves.
When Ralph is visiting his parent before dinner with the Hurleys and his mother turn on one lamp, the room remains fairly dark. On the next cut, which is a closeup of Ralph's mother, the room is now completely bright.
Real-life radio soap opera "The Romance of Helen Trent" is heard on the radio while Hurley family members are waking up, eating breakfast, and preparing to leave for work. In reality, radio soaps weren't broadcast until late mornings, afternoons, or evenings.
Aggie says they only had five days' notice until the wedding. They found out about the wedding on Friday morning. The wedding is scheduled for Tuesday morning. That is four days.
However, different cultures may count the passage of days differently. Think of the Christian belief of Christ rising from the dead after 3 days. He was crucified Friday afternoon and rose on Sunday morning - less than two full days. The count of 3 days comes from parts of Friday and Sunday, with only a full day on Saturday.
The days and dates mentioned in the film only work if the year is 1951 or 1956. The license plates of the taxis all show a year of 1955.
The year is 1956. Car registrations expire after one year; therefore, seeing 1955 license plates in 1956 is to be expected.
It is obvious that there is no glass in the Hotel Caterer's office.