Delay time depends on gap status. in Al it can be less as compared to other metals like steel. I hope i answer your question.

the unit is micro sec.

The delay arises thereafter, how stable is the machining process. Primarily it is therefore independent of the material used. On the other hand special materials cause the working gap becomes contaminated very quickly, so that the process parameters, such as flushing, pulse parameters and control parameters have to be changed.

An important factor in the consideration of the delay time is whether they will be evaluated and the process control plays a role. The measured sizes are in the microsecond range, while the real sizes can be found in the 100ns range (measuring problem!).

Delay time also known as pulse pause time allows the deionisation and thereby subsequent ionisation cycle. more delay time ensures complete deionisation and hence requires more energy for subsequent ionisation and rest of the energy would be expensed in metling. Aluminium being low melting temp material having higher thermal conductivity starts melting rapidly and size of crater formed would be large and deep. 

This is wrong, the delay time is not break time, but the delay of the breakdown after applying the full ignition voltage. She stands for process reasons (gap contamination) and is greater, the better the working gap has been decontaminated (in the pause duration). we have almost no delay period, then there is a high contamination gap, the pulse ignites before the actual starting voltage is reached and there is a risk of an arc (which is not desired).

The delay time can be measured and used as a control variable. It is true that the aluminum produced very specific contamination, the surface oxidizes quickly and the surface tension of the liquid aluminum plays a special role in the formation of the surface topology.

Sorry, my experience is on water flows.

 Yes, in case of single pulse discharge characteristics, it is the delay of the breakdown after the applying full ignition voltage.

However, i have come across few scholars/Researchers using the same word delay in place of pulse off time ( pause time).  they used to refer it as delay time for the subsequent ionisation. and hence i trie to explain the mechanics. 

i have worked out the various time elemts for single discharge characteristic for EDM discharge.

as attached for reference. 

the during delay time, nearby dielectric fluid gets agitated and bcs of he floating contaminants and some impurities in the fluid, which tend to disturb the voltage potential, it delay the actual breakdown of the fluid.

The problem with the parameter naming is that no real standardization exists, and so each introduces its own terms.

So I think it is completely inappropriate to describe the erosion duration with ton. This name comes from the electronics, but the release of the energy pulse must not necessarily be connected to the opening of a transistor.

Her sample: Here they have a relaxation generator (RC - process power source) since the names are partly unlike static pulse generators or needle pulse generators (with or without ignition stage).

I suppose that their scale of voltage axis not quite right, because the (arc voltage) is usually significantly lower than the ignition voltage (open circuit voltage). The operating voltage to be called arc voltage is wrong when they consider the EDM. Depending on the process, the burning voltage a spark, an arc or an abnormal arc voltage be.

The charging of the capacitor goes until the breakdown conditions are met in the working gap. Normally the ignition voltage is never reached and the optimum is at 72% of the ignition voltage. Optimum because this charging time and reached ignition voltage are interdependent.

Your subdivision in charging time 1 and 2 ionization time I do not quite understand. It is also for the energetic considerations not relevant.

For a more accurate indication of the time parameters it would be better to show the corresponding current flow.

When RC generator so there is no delay time 3, because the duration is 3, the breakdown to the channeling. A delay time in the static pulse generator is present when the ignition voltage is reached and still no current is measured.

Thus, their statement that the ON time includes the time periods 1 to 5 is incorrect. Consider the pulse duration as the period where energy is introduced into the system ignition / sparks / collapse, then it is only the time sections 3 to 4 (5). Section 5 also corresponds not deionisation duration but follows from the resonance conditions and the parasitic elements of the working group (gap - feed line - contact). De-ioniseren is their system a priority in the period. 7