Corrected entry: The time of year changes throughout the action. When Parker Posey is grilling chicken outside her house, she's wearing a coat and the trees are bare. But in the scene on the courthouse lawn a few minutes later, the singers are all wearing T-shirts. And at the end of the movie, we learn that Mort Guffman's flight couldn't leave New York because of a snowstorm there.
Corrected entry: At The Chinese dinner, the plate of beef disappears then reappears.
Correction: The movie at this time is in chronological order with no edits, but a somewhat flexible camera. A waitress is constantly bringing in new items, and Catherine O'Hara is bombed, soused, smashed, etc. beyond belief. It's very possible that when Dr Pearl was talking, it got moved to another part of the table, then got moved back for any one of Albertsons (Ron or Sheila), or Pearls (Allan or his wife) to grab some more.
Correction: The film was shot in 29 days in Lockhart, Texas (the town is supposed to be in Missouri). Some trees are bare, but the grass is green, so it's early spring. Not to hard to believe that it would be chilly at morning/evening with short sleeve weather (at least for kids) in the middle of the day, but still possibility of snow in New York.