For any AA type cells you will not want to use a high charge rate like 2A, unless the cells are specifically rated for that kind of current. Typically about 1A is going to be the max you would want to push them. I know this is not a fast charge like you would want at the track, but most smaller cells simply cant handle it. I believe some of the 2/3A cells might be able to handle higher rates, but check with the manufacturers.

For overnight charging you will want as low as possible current, I believe your charger goes down to 0.1A.

The 1.2V rating on the cells is just a nominal rating, meaning they "should" hold about 1.2V average while discharging. While charging it is not uncommon to see voltages go well beyond 6V.

The auto setting on your charger should be accessed by pressing both left and right directional buttons from the current setup screen. Then you simply set the maximum current you want and the charger will determine the best rate up to your max.

I hope this helps, but Im sure you will get more responses if not.