"Either today or never!"
Translation:Ή σήμερα ή ποτέ!
The audio on the 'Η isn't an 'ee' sound but a 'eetatonos' or something. Is this correct?
That is not how the word is pronounced in the sentence, so in that sense it's not correct.
I imagine you saw this on the Android app while tapping a tile -- in that case, the text-to-speech voice doesn't have the context of the sentence, and seems to be prone to treating single-letter words as letters rather than words, so it may have read ή not as /i/ but as /ita tonos/, i.e. "letter eta with tonos [accent mark]".
The pronunciation as a word is simple /i/ (pretty much like the name of the English letter E).