Mr. Kramer's lawyer tells him that, if he wishes to appeal the decision granting custody to his ex-wife, his son would have to take the stand. On an appeal, no new evidence is called, and therefore the son would not be called as a witness.
When Ted is first making French Toast, he picks up the egg in his right hand; when he shows it to Billy before breaking it, it's in his left hand; when the camera goes to closeup as he breaks the egg, it's back in his right hand. Dustin Hoffman's disheveled hair also changes wildly in that scene.
Ted's job interview takes place at 4pm on Friday, Dec.22nd (during the office Christmas party). The next scene has Ted and Billy visiting Ted's 'new' office. Ted tells Billy "It's Saturday, most people take the day off".
Ted's office already has his name plate, pictures of Billy on the wall, and work assignments.
This could only be true if a week had passed between the 2 scenes.
Dustin Hoffman pours raw egg & milk mixture into the pan while making the french toast. Later the pan contents burn. The close-up shows it all as browning. After that close-up Hoffman drops the pan on the floor. The egg and milk mixture flies out, and it is raw again.
When Billy wakes Ted the morning after the separation there is a yellow Trimline phone on the bedside table. Later that morning when Ted calls home from the office there is now a beige Princess style phone sitting on the bed.
When Ted goes to apply for a job, the date is Friday, December 22. Near the end of the film when Ted's lawyer reads the court ruling, the ruling is dated Monday, January 23. If December 22 was a Friday (as it was in 1978), then it's impossible that January 23 fell on a Monday. In fact, the next time January 23 fell on a Monday wasn't until 1984.