Seems like a two month process....
Converting to Biodiesel
When starting to use biodiesel in vehicles that have been running on mineral diesel, biodiesel should be introduced gradually as described above. Starting with a blend of approximately 5% biodiesel. Therefore, before filling up, you need to have a reasonable idea of the capacity of your fuel tank. Most vehicle handbooks will specify the size in litres. Then calculate 5% of the capacity e.g. if your tank holds 50 litres, 5% is 2.5 litres. Put in biodiesel up to 5 % of the capacity of the tank and then fill up with mineral diesel.
Depending on your type of vehicle (see list of biodiesel compatible vehicles) you can either continue using a 5% blend each time you re-fill or gradually increase the biodiesel blend ratio to your chosen level. If you decide to use a higher percentage of biodiesel, the rate at which you increase it is up to your judgement but, for example, it could be:- first tank 5%, second tank 10%, third tank 20%, fourth tank 40%, fifth tank 60%, sixth tank 80%, seventh and subsequent tanks 100%.
When you have reached your required level, you can switch freely between that level and 100% mineral diesel as required. You would only need to repeat the introduction process should you use mineral diesel consistently for a prolonged period.