Come ottenere la differenza tra due date arrotondate alle ore

select time_to_sec(timediff('2010-09-01 03:00:00', '2010-09-01 00:10:00' )) / 3600;

+-----------------------------------------------------------------------------+
| time_to_sec(timediff('2010-09-01 03:00:00', '2010-09-01 00:10:00' )) / 3600 |
+-----------------------------------------------------------------------------+
|                                                                      2.8333 | 
+-----------------------------------------------------------------------------+