It is not negative.
any time less than 9 seconds is shown as
-1 -2 -5 -9 instead of 01 02 05 09.
Your Data usage is counted.
Even if it so, time you were logged in
does not matter, as usage charges are not time based.
But start time is 8:11:04 and stop time is 8:11:00 (on 25.09.2009).
so the time calculated acc. to bsnl is -4.
And therefore -4 represents negative 4 not 04