Best Buy orders can typically be canceled up to thirty (30) minutes after the order has been placed. If an item is on backorder, it can be canceled at any time while it is still on backorder. To check if an order can be canceled, check the order status on BestBuy.com.
If there is a cancel button on the bottom right side of the order status screen, the order can still be canceled. Here are the steps to cancel an order.