There is no direct flight from Heathrow to Cincinnati so the travel time would depend on the time at the connecting airport.
8 or 9 hours
exactly 8 hours 42 minutes 11 seconds and 39 milliseconds on Jetstar. exactly 8 hours 23 minutes 15 seconds and 52 milliseconds on Webjet. exactly 9 hours 54 minutes 39 seconds and 22 milliseconds on...
12 hours
LHR - BOM NonstopFlt AI144 08hr 30min Air IndiaFlt 77W 08hr 50min Jet AirwaysFlt 08 09hr 00min Kingfisher