So your sentence we start tomorrow is proper in this context.if meant to be a question a question mark should be added, we start. I have been poking around wondering about the colloquial usage of on tomorrow in southern american english and wondering about. You can say, do you work on tuesdays?
KNWA Weather and Fox 24 Weather with Dan Skoff and Rick Katzfey
Tomorrow morning is idiomatic english, tomorrow's morning isn't.
