season | episodes | time slot (est) | season premiere | season finale | tv season | rank | viewers (in millions) |
1 | 23 | wednesday 10 pm / 9c | september 22 , 2004 | may 18 , 2005 | 2004 - 2005 | 21 | 13.59 |
2 | 24 | wednesday 10 pm / 9c | september 28 , 2005 | may 17 , 2006 | 2005 - 2006 | 22 | 14.04 |
3 | 24 | wednesday 10 pm / 9c | september 20 , 2006 | may 16 , 2007 | 2006 - 2007 | 25 | 13.92 |
4 | 21 | wednesday 10 pm / 9c | september 26 , 2007 | may 21 , 2008 | 2007 - 2008 | 28 | 11.71 |
5 | 25 | wednesday 10 pm / 9c | september 24 , 2008 | may 14 , 2009 | 2008 - 2009 | 17 | 13.5 |
6 | 23 | wednesday 10 pm / 9c | september 23 , 2009 | may 26 , 2010 | 2009 - 2010 | 23 | 12.66 |
7 | 22 | friday 9 pm / 8c | september 24 , 2010 | may 13 , 2011 | 2010 - 2011 | 37 | 10.73 |
8 | 18 | friday 9 pm / 8c | september 23 , 2011 | may 11 , 2012 | 2011 - 2012 | 38 | 10.34 |