There are times when both 五日 (5th day of the month) and 何時か (someday) could be used I think. Does this become a minor problem for Japanese when speaking (no kanji to guide), or do they speak in some way to avoid the possible confusion?
A sentence I thought of where either いつか could be possible:
いつか、アメリカに行きます。
Are they going to America on the 5th of the month, or are they expressing intent to go to America eventually in the future?