Deals always end Saturday. March 1st is the last day of the deal...
Edit: I realize now I said May. But I believe it's actually ending in March. I think this is the last batch if I recall correctly.
The physical coupon code is different than the online code. So in short no you can not use it in store. If you have the numbers from the physical coupon you might be able to get them to punch it in for you.
You misunderstood, the coupon is 20 dollars off of live if you buy a console at the same time. Unless you need a second xbox one it's not a deal for you.