Just read Hans's post in the "what did you do..." thread re diff fluid change. I too just finished changing fluids and filters but I didn't do the diff or the hubs. The differential fluid was changing about 5 years ago. How often is everyone changing these two? Thanks.
jor
PS: Marjet is setting the bar pretty high!
I would look at it both by time AND miles.
Probably 5 years or 75,000 miles. If front hub shows signs of contamination (clear plastic window will show it once center cap removed) immediately. But, one quart of oil will change both front hubs a couple of times.
I changed out my OE hub caps for one with a removable center, making it easier to check on a regular basis.