Does it hurt to charge the batteries while they are in use: Generally NO.
With that charger I'd say NO
HOWEver that sounds like a basic charger. NOT a "Smart" charger, this means it puts current even when the batteries are full up. Overcharging and doing damage. |At least on the 10 am setting it MIGHT.. Of course if you have enough battery.. it won't matter.
I would seriously consider a Progressibe Dynamivcs 91xx (not sure the smallest model) plug in model.. Those. you can leave hooked up and plugged in for up to about a decade give or take a bit..Both in use and not in use.