Not enough time, IMO. If you are coming from outside of Europe you will be jet lagged and unlikely to arrive in any Dolomites town close to hiking by noon. I certainly would not recommend driving after an overnight flight. If you are already in Europe it is slightly better, of course, so LMK!
You can get to Bolzano in 2.5 to 4.5 hours by train from Venice. That is sort of a kicking off point for the mountains as it is in the valley. You can go further by bus to Castelrotto or one of the Val Gardena towns for a better mountain experience. You will be lucky to check in by mid afternoon, I think, so maybe a short hike as days are long in August although afternoon thunderstorms are the norm.
With only one full day allocated, what if it is raining that day? Would you still hike?
You can go back to Bolzano to catch a high speed train.