un giorno o l'altro bedeutet auf Englisch

one day▼(at unspecified time in the future)
adverb
[UK: wʌn deɪ] [US: wʌn ˈdeɪ]

sometime▼(at an indefinite but stated time in the past or future)
adverb
[UK: ˈsʌm.taɪm] [US: ˈsʌm.ˌtaɪm]