About 3 to 3½ hours via I75 depending on traffic through Dayton.
Interstate 75 is the fastest route between Dayton and Cincinnati. The question above does not include a reference to the route one is approaching I 75. But the trip from Dayton to Cincinnati is about 50 miles. From the outer belt of Dayton (675) and the outer belt of Cincinnati (275) it is only about a 30 minute drive at most.
not sure
1 week
www.mapquest.com
It takes about 15.5 hours to drive from Dayton, Oregon to Los Angeles, California.
about 2 days
about 3-5 hours depends what route you take
4-5 hrs
About 3.5 hours.
too long grab a flight
Depending on when what time of day the letter is mailed and where specifically the letter is posted in Dayton, and where specifically the letter is sent in Cincinnati, it could be as little as the next day, or as long as three business days. However, most likely the letter will take two business days to make the trip.