When Lois and Clark arrive home in the last scene Clark says it was an interesting birthday. But his birthday was the day before, the whole story clearly takes place over 3 days. It opens the night before his birthday, the day of his birthday starts with the charity golf game and ends with the oil fire and the day after his birthday they are at the office, then go out to dinner for Chinese food and then the shuttle launch.
When Lois is trying to plan a surprise birthday party for Clark she uses the cover of the Ladies Overseas Aide inviting Superman to speak at their charity event. But if that plan had worked he would have showed up to the party as Superman and not as Clark.