Mooyo: I don't think the plans are pro-rated at all, they weren't when I worked there thats for sure. Might also be different expecially if your at the main store there in MN.
I work at the Burnsville store which is about 10-15 minutes away. Policies shouldn't differ throughout the stores anyway it just depends on the management. There's been a few plans I myself have returned (things I had bought but decided to sell to friends or family and had already bought service plans on). I don't see customers take advantage of it that often but it is written in the plan
"...This Plan can be cancelled by you at any time for any reason by sending to us notice of cancellation: (a) within thirty (30) days of the receipt of this Plan, you shall receive a full refund of the price paid for the Plan provided no service has been performed, or (b) after thirty (30) days, you will recieve a pro rata refund, less the cost of any service received."