Is any content in Stardew Valley permanently locked to a specific time window?

Solution 1:

Though they aren't time locked, there are a couple permanently missable events I was able to find on a wiki.

  • Clint's 6 heart event will not trigger if you've already seen Emily's 8 or 10 heart event, or are married to her.
  • Penny's 4 heart event will not trigger if you have bought the "Community Upgrade" at Robin's after finishing the community center.

Also, while it isn't an "event", purchasing wood and stone at the Carpenter's Shop or coal and ore at the Blacksmith becomes more expensive after the first year has concluded.