Grep doesn't parse timestamps, and neither will your AWK script. You're going to need something more intelligent.
Some Linux distros came with a log viewer app that might be able to help, but I don't know what's available at the moment. I think the viewer may have been named something like "sawmill".
Failing that, you could write a perl or python script that parsed the dates and filtered lines. Or, for that matter, a Java Application using the DateParser class. Probably doable in about 100 lines of Java.
AWK might be able to handle the date parsing, too, but it would be a lot of work, I think.
Customer surveys are for companies who didn't pay proper attention to begin with.