Two answers really:
1: Anytime you increase the workload, you lengthen the time it takes to peak.
2: EMS can work in two different ways;
A: A few EMS sessions can actually change the tone of muscles in a heavy training phase by recruiting above the voluntary capacity, thus shifting the on/off fibre proportion cycling back towards what you would see closer to the competition phase.
B: A longer EMS phase will lead to higher training loads in the muscles involved. I now feel that this type of EMS is best reserved for areas that require specific strengthening/attention.