Unfortunately, all points must be redeemed prior to check-in for your stay. Once you have checked in, you will not be able to redeem your points.
When you redeem your points, you will also make a reservation at the same time. You will then need to scan your Spot Club card or the app at check-in and checkout in order for your reservation/point redemption to link to your stay. If you have already checked in, you will not be able to do this and if a reservation has been made after checking in, it will not be valid at checkout.