To the OP - that sounds reasonable. I tend to go 2-4 weeks between chain lubes depending on weather conditions. I use Finish Line wet, and clean the cogs, between the gogs, and the rear derailleur w/ a rag, too. (Park Tools cleaning brush is in the mail and will hopefully aid significantly). When it's really sloppy, I've occasionally done it with as little as one week between lubes, but I was using crappier lube then and didn't have fenders yet.

As others have said, if it's chirping or looks really dry, those are also signs it's time for another lube.