PHEV on-board charger limits current at 14A, so typical power delivered to empty battery is about 3 kW max (with factory cable it is 2.0 kW or so).
During charging, PHEV has two special periods, used to prebalancing, with length of about 15 minutes, where charging is reduced to 0,2 kW (10x slower). This prebalancing has some sense, if you focus on charging battery a bit (like up to max 80%). There is no reason to do that (and loose time) if you need your car quickly charged, and final balancing can be processed overnight.
Accelev cancels both these periods, and postpones prebalancing to the last, slow phase of charging. This saves a lot of time – for example with 16A charger you will measure about 2.2 kW charged within first hour (first prebalancing occur after 10-20 minutes from start of charging of empty battery). And with Accelev – 3,5 kW.
This explains additional time gain for Accelev – it saves about 25 minutes (slightly less than half an hour) extra due to postponing prebalancing to the last charging phase (night phase).
This is valid for all PHEV model years – 2013- 2018.