If the EVSE has a high enough current limit, there is no difference in charging time between 208 and 240 volts because the onboard charger will draw more current to compensate for the lower voltage. With a 3.3 kW onboard charger, there will be no difference in charging time as long as the EVSE allows at least 18 amperes. With a 30-ampere EVSE and 6 kW onboard charger, charging times will be slightly less at 240 volts because the charger will draw about 27 amperes at 240 and 30 amperes (current limit of EVSE) at 208 (6480 W input at 240 volts and 6240 W input at 208 volts). The difference in time is only about 4 percent. If the EVSE has a lower current limit, then the charging time would be 13 percent less at 240 vs. 208 volts (208/240=0.867).
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL+ purchased 8/10/2019