Giant unilamellar vesicle is the closest prototypical model for investigating membrane electrodeformation and electroporation in biological cells. This work employs numerical simulations to investigate the effect of membrane charging time on vesicle electroporation under milli-second pulsed-electric-field (msPEF) of different waveforms. Our numerical approach, which implements the effect of electric stretching on membrane tension and precise calculation of pore energy, successfully predicts the formation of giant pores of O(1)μm size as observed in previous experiments. The poration zone is found to extend up to certain angles as measured from the poles, termed critical angles. An increase in charging time delays pore formation, decreases the pore density, and trims down the poration zone. Counterintuitively, this effect promotes significant pore growth. Moreover, there exists a cut-off charging time above which pore formation is completely inhibited. This phenomenon is particularly pronounced with square bipolar pulses. Comparisons with the previous experimental results reveal that electrodeformation-poration-induced membrane surface area variation and that induced only by electroporation evolves in a similar fashion. Therefore, although the agreements are qualitative, the present electroporation model can be used as the simplest tool to predict the evolution of vesicles under electric pulses in laboratory experiments.