If you are an American citizen, you have significantly skewed how US tax works. You always are required to report worldwide income no matter how much time you are in the US. While abroad, you have reliefs available to you and some of them require you to met a time test. Maybe this is what you are thinking of? By waiting to meet the time test, it just means you file your return later not that these aren't available to you at all.
If you are an NRA, the story changes.