We recommend performing a full bleed and replacing the mineral oil at least every 2 years.
The main reason for that longer interval compared to our DOT brakes is that mineral oil does not absorb moisture.
Shorter intervals of time between bleeds may be required if you ride frequently, ride on aggressive terrain that requires heavy braking, and/or in sub-freezing temperatures.
Here you can find our DB8 bleed manual or just visit our SRAM TECH YouTube Channel.