I usually take my position in line when that group of 30 is about 2 or 3 minutes from being called. So if I have an A45 (about average for me) I line up about 2/3rd of the way through A15-A30 boarding. People seem to get annoyed or assume that I am a line jumper/Kettle/noob who is trying to sneak my way into a good spot but I think they are silly for standing around for 25 minutes.