"I was working day and night."
Translation:Я работал день и ночь.
«Днём и но́чью» should work too (if it's not, please report it).
However, mixing these forms doesn't sound good: using different cases makes the reader think those have different grammatical meanings. «Я рабо́тал(а) днём и ночь» would be understood to mean something like "I was working the night during the day too", which is pretty meaningless (techinally 'работать' can be used as a transitive verb meaning 'to create, to produce', but this is a very rare meaning not used in modern Russian, and you probably don't produce nights when you work anyway).
«Работала» is used when the person working is female, or denoted a feminine noun, «работал» is used when the person working was male, or denoted by a masculine noun. There's also «рабо́тало» for neuter nouns.