01,02530,2011-01-26,08:11:00,IN
01,02530,2011-01-26,18:40:00,OUT
01,02801,2011-01-26,09:07:00,IN
01,02801,2011-01-26,09:47:00,OUT
01,02801,2011-01-26,09:53:00,IN
01,02801,2011-01-26,18:06:00,OUT
01,02877,2011-01-26,08:29:00,IN
01,02877,2011-01-26,17:11:00,OUT
01,05713,2011-01-26,08:11:00,IN
01,05713,2011-01-26,13:47:00,OUT
01,05713,2011-01-26,14:47:00,IN
01,05713,2011-01-26,17:08:00,OUT

awk -F, '{if($1 != "X" && !a[$3]) {a[$3]++;if($4 > "09:10:00") print "ID number " $2 " came in on",substr($3,6,5)," at",substr($4,0,5),"after 09:10";}}'

$1 != "X" &&

Originally Posted by anurag.singh

1. $1 != "X" == >> $1 is 1st field of every record, This check ensures that we should not process 1st record in inputFIle, The Header Record (X , ID , Date, Time, Y
). But this check is not necessary(And can be removed) in post #10 command. 2nd if condition (check on $4) will not be true for Header record and so that will not be printed.
2. what does !a[$3] stand for? == >> This checks if a[$3] is NULL OR has any value set in it. if(!a[$3]) is equivalent to if(a[$3]==NULL)
3. substr($3,6,5) == >> $3 will have year value like 2010-12-03. String indices in awk starts at 1. To get 12-03, start index is 6 (12-03 starts from 6th character) and then it goes upto the end i.e. lenght is 5.
substr($3,6) also gives same result. length is not needed if substring goes upto the last character.

I learned most of stuffs here only (After building few basics) by following posts of experts here Scrutinizer, vgersh99, Franklin52, fpmurphy, scottn, radoulov etc to name a few

Few AWK articles (Many more can be found on internet):
opengroup_awk
grymoire
Utrecht_University_docs
thegeekstuff_awk_with_examples (link removed)