It should update more frequently than once a month, but because of higher priorities and possibly grumpy software/hardware it hasn't been that often lately. It'll probably update today now that I've said that
It should be somewhat about every 6 to 10 days or so. It gets updated soon after a new RDF file is produced, and is updated from that RDF file. Sometimes a new RDF file may have errors and is dumped in the Bit Bucket, and the older version reinstated instead. I would be surprised if more than three weeks passed without an update (unless there is scheduled downtime or a major bug somewhere - like at present).