Upvote:4
I can't answer for all airlines, but for the airline I work for (one of the US big 3), the answer is No. We regularly use the same flight number for multiple flights in a day but when that happens they are guaranteed to be departing from different airports at different times. Sometimes we use the same equipment, but sometimes the same flight number can hop to a different aircraft. It seems like a reasonable guess that other major airlines would take the same approach, if for no other reason than having multiple flights with the same number leaving from the same airport in a day would make crunching the numbers (i.e. looking at revenue, number of pax, etc) much harder after the fact.