Dear Friend,

    Hope this will give you a clear Idea. Please follow the link.

http://www.dieselmotors.info/fuel-systems/diesel-engine-injector-pump-timing.html

For viscous edible & non edible oils having more delay period, advancing IT [diesel IT 20 bTDC] gives more time to form combustible mix so that Peak pressure is just after TDC. For biodiesels same as diesel.

Hence more IT advance means more delay period &  more IT retarding means less delay period.However experimentation is final solution where all other properties are automatically considered during variations of operating conditions.  

This can be known by instrumenting your injector through fixing a needle lift transducer on top of the needle which will indicate the moment when the needle start lifting which correspond to the start of injection. Then  use another pressure transducer to measure the cylinder pressure variation with crank angle( you may take the average of 50 cycles when recording data via a data logger). Then when you draw Cylinder pressure against crank  angle you note a kink in the Pressre-CA curve after the injection timing which indicates the moment at which combustion started ( in crank angle degrees). The by knowing both the start of injection and start of combustion you may subtract to get the delay period in CA degrees.