It depends on a few factors: how many Play Kits you were gifted, when you choose to activate it, and how you choose to use it.
If you choose to apply it toward an existing Pay per Kit subscription, the gift will apply to the Kit that is scheduled to ship next.
If you add the gift to a Prepay & Save subscription, the gift will apply to the Kits that ship immediately after the delivery of your final prepaid Kit.
If you don’t have an active subscription, you can still review the details of any future shipments in your account.