Time capturing

Hi,
I have a requirement where in i need to capture time taken by the user to enter the data in a cell.
For eg.,, if user starts entering data in A1 and if the text is Testing.
The moment he enter T, we need to capture the time and when he completes entering the test we need to capture one more time.

It should like like this.
A1 B1 C1
Testing 19/11/2008 07:45:44 19/11/2008 07:45:50

Can some one please help.


Thanks,
Jai