I have got confused, ms generally means millisecond but in the snapshots I have seen it being used as microsecond. Am I correct or is it millisecond only?

How about a bit of RTFM? The second hit when searching for "direct reads elapsed time" is this one:
http://publib.boulder.ibm.com/infoce.../r0001264.html

Hi stolze,
my question was not particular to direct reads elapsed time. sometimes I have seen that while using table functions for snapshot there are elements which are broken into two , one for seconds and another for microsecond.for eg : ELAPSED_EXEC_TIME_S
ELAPSED_EXEC_TIME_MS where MS is microsecond. So I got confused as at one place its saying its millisecond and at another its microsecond.

When you do a snapshot for dynamic SQL, you get the elapsed time in the following format:

nn.nnnnnn seconds

So I assume that for the snapshot table function, you should divide ELAPSED_EXEC_TIME_MS by 1000000 to get the right answer.