Native English speakers don’t pronounce the ‘o’ vowel in the 1st syllable

The term I know is Vowel reduction.

I would be very surprised if you pronounced the word [toˈde] ("toe day"), but I could imagine someone saying [tuˈde] ("2 day"). There is no analysis-neutral name for such a pronunciation, but it could be labeled a "spelling pronunciation" or a "dialect pronunciation". It would normally be pronounced as [tuˈde] in Kenyan English, so it can indeed be a dialect feature, and if you're Kenyan, then that's just the way it is. It could be based on the fact that the "to" component of the word (originally, the phrase "to day") is pronounced [tu] at least when stressed, and spelling can influence pronunciation.