The internet has a range of values from 3 months to a year, depending largely on the political/economic interest of the site in question. Here's a couple quotes that you might want to follow up on:
From springboardbiodiesel,
The truth is that all fuels will degrade over time. In fact, the EPA
reports that ULSD diesel has a shelf life of between 3-6 months.
Biodiesel, too, has a shelf life that can vary significantly, but with
the proper fuel management, biodiesel's shelf life can be extended
dramatically.
The biggest factors that affect biodiesel storage life include:
Microbial contamination Chemical contamination Exposure to light
Temperature Exposure to air The type of feedstock And the additives
From BellPerformance,
All fuels degrade over time. The old school diesel fuels from the
fifties could be kept relatively fresh for 1-2 years. The advent of
ultra low sulfur diesel cut this storage to 3-6 months. When you blend
biodiesel into the mix, the figure changes again. So there's no one
stock answer to the question. A fuel's storage life is going to depend
on a host of factors related to storage conditions.
The influencers of storage life for both conventional diesel and
biodiesel would be contamination with microbes and/or chemicals,
light, storage temperature, oxygen exposure, and the type of biodiesel
feedstock that the fuel was made from.
From AssociatedPetroleum,
Most fuel today is used up long before six months, and many petroleum
companies do not recommend storing petroleum diesel for more than six
months. The current industry recommendation is that biodiesel be used
within six months, or reanalyzed after six months to ensure the fuel
meets ASTM specifications (D-6751). A longer shelf life is possible
depending on the fuel composition and the use of storage enhancing
additives.
At the risk of getting booted off this forum, YMMV :-)
