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Once you've changed it the first time, you can drive it until it starts
failing the 'parking lot test'. When you start hearing a moaning,
scraping noise when you turn a sharp left-hand turn at low speed, then
it's time to change it. The sound may not even sound like it's from the
rear end, sometimes like a dragging front brake, but that's it. On the
CR-V, which uses a different fluid but for the same purpose, the
interval has been determined to be 50,000 Km (30,000 miles).
The first change is the most important one, since it has the most
impurities in the fluid.

'Curly'

Direct quotes from Honda Service Recommendations.
Normal Service:
o Replace VTM-4 rear differential fluid, first replacement at 15,000, then
at 30,000 miles (24,000 km, then 48,000 km) or 1 year, then every 30,000
miles (48,000 km) or 2 years.

o Capacity: 2.64 L (2.79 US qt), use Honda VTM-4 differential fluid.

Severe Service:

o Replace VTM-4 rear differential fluid, first replacement at 7,500 then at
15,000 miles (12,000 km, then 24,000 km) or 6 months, then every 15,000
miles (24,000 km) or 1 year.

 a.. Capacity: 2.64 L (2.79 US qt), use Honda VTM-4 differential fluid.

 b.. Follow this schedule for rear differential fluid replacement if you
use your vehicle for off-highway driving, trailer towing, mainly in
stop-and-go driving. Otherwise, use the fluid replacement schedule in the
Maintenance Schedule for Normal Conditions.

I hope this answers your question!