date in log file?

Dear Sirs/Madams,

I always have debug logging on, one thing got me thinking tonight, how do i tell what date in the log file something is logged?

I can clearly see the time something is logged, but if the log has not rotated in a while, what is the easiest way of telling what the date something was logged?

Does these figures mean aything? T:139776546334848

Many thanks for any input!

Best Regards
Patric