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Pellet ELM triggering is a well established scheme for decreasing the timebetween two successive ELM crashes below its natural value. Reliable ELM pacinghas been demonstrated experimentally in several devices increasing the ELMfrequency considerably. However, it was also shown that the frequency cannot beincreased arbitrarily due to a so-called lag-time. During this time after apreceding natural or triggered ELM crash, neither a natural ELM crash occursnor the triggering of an ELM crash by pellet injection is possible. For thisarticle, pellet ELM triggering simulations are advanced beyond previous studiesin two ways. Firstly, realistic ExB and diamagnetic background flows areincluded. And secondly, the pellet is injected at different stages of thepedestal build-up. This allows to recover the lag-time for the first time insimulations and investigate it in detail. A series of non-linear extended MHDsimulations is performed to investigate the plasma dynamics resulting from aninjection at different time points during the pedestal build-up. Theexperimentally observed lag-time is qualitatively reproduced well. Inparticular, a sharp transition is observed between the regime where no ELMs canbe triggered and the regime where pellet injection causes an ELM crash. Viavariations of pellet parameters and injection time, the two regimes are studiedand compared in detail revealing pronounced differences in the non-lineardynamics. The toroidal mode spectrum is significantly broader when an ELM crashis triggered enhancing the stochasticity and therefore also the losses ofthermal energy along magnetic field lines. In the heat fluxes to the divertortargets, pronounced toroidal asymmetries are observed. In case of highinjection velocities leading to deep penetration, also the excitation of coremodes like the $2/1$ neoclassical tearing mode is observed.

Transition from no-ELM response to pellet ELM triggering during pedestal build-up -- insights from extended MHD simulations