Trace file doubt

Hi all,

I am new to Ns2, I have ran some simple example on ns2 where I added CBR
traffic with packet size 500 and interval 0.010. what is the units of the
packet size and interval. I think it is KB and ms. Please confirm.

My second question is that what is the meaning of time in trace file 2nd
column. what it signifies in my case it is incremented by 0.005ms always.
how it can be changed. Actually I am trying to measure average end to end
delay from the tutorial below.

http://ns2ultimate.tumblr.com/post/5240359082/post-processing-ns2-result-using-ns2-trace-ex3

I am not understanding how the delay is calculated in this link. The
difference between the current time(receive time) and '+' time are added at
each link or for src to dst for all the link divided by number of link
between the src to dst pair.

How can I add warm up time to the network? and how can I continue
simulation till the last packet?

Thanks,
pakhi