When you can get the line number you can tell awk as well as sed to start on this line. But I dunno how. But should not be hard to check how to do this.
Some other ideas on this.
1.) Hourly cron job (maybe calling a perl script)
1a) Get size of file (and write to file)
1b) Find the difference between the last file size and the new one
1c) Extract the lines
1d) Parse files
1.) Hourly cron job (bash script)
1a) grep $cur_date:$cur_hour-1 > /tmp/file
1b) Parse files
I once had a perl programm which did exactly what you need but can't find it anymore
P.S. Funny your LQ Post in fourth on google searching for "hourly parse log file linux"