Orders can be canceled at any time before they reach the Shipped status. Note, however that under current PayPal policy, PayPal no longer refunds the fees that sellers pay when a purchase is made through that platform. If you paid using PayPal, and subsequently cancel your order, the PayPal fees associated with your order (currently $0.30 + 2.9% of the total amount) will be withheld from your refund. This policy can be seen at the link below:
Under the section titled "Other Online Merchant Fees", it reads in part "If you refund (partially or fully) a transaction to a buyer or a donation to a donor, there are no fees to make the refund, but the fees you originally paid as the seller will not be returned to you." (emphasis added).