G'day natxo,

Would this be a simpler solution for what you're trying to achieve?

$ perl -nle 'next unless /^(.*?) INFO .*? SENT/; $x = $1; END { print 
+$x }'
ts1 INFO ... SENT
ts2 INFO ... RECV
ts3 INFO ... SENT
ts4 INFO ... RECV
ts3
[download]

Skip unless match, otherwise save capture. Print last capture at the end.

I used STDIN (keyboard) for dummy logfile records:

ts1 INFO ... SENT
ts2 INFO ... RECV
ts3 INFO ... SENT
ts4 INFO ... RECV
[download]

Output last matching timestamp: ts3