Pair or single wouldn't matter in the WP2/SP2 chargers; Independent channels. 2 hours would be about right for that current and capacity.
On a completely depleted battery perhaps, but not if the individual quit when the battery started to wane at 3.5V or even allowed it to go to an anemic vape at 3.2.
I have used the gamut of XTars and they may have independent channels for monitoring but on "X setting" "X" is divided by the amount of cells being charged. e.g charging 2 batts at 1A = 500mAh per cell. Once one cell is charged, the remaining current will go to the cell still requiring a charge and, albeit 1A is available, the charger will deliver the optimum to the cell and that optimum may not necessarily be 1A depending on the charge state of the battery.
WRT the WP2, the right channel is a trickle between being charged at the full 500mA or a factor thereof. IOW charge curent varies between channels with the left channel being the main charge channel, during the charge cycle.
On the WP6 although the charger has 6 bays, it is constructed of 3 x WP2 pairs with each left channel of the pair being the main charging channel. IOW to take full advantage of the chargers charging capability when charging lets say 2 x 18650, you would place your batteries in bay 1 &3 and skip bay#2. The 2A charging current is fixed and divided between the cells being charged. That is my experience with these chargers.
