FedEx delivery drivers will make up to 3 delivery attempts to deliver the package but not in one day.
The Delivery attempts will happen over the course of 3 business days and if you're still unavailable to sign for the package they will return the package to the shipper.
FedEx should leave a door tag on your door stating they attempted delivery and if you sign that door tag giving them permission to leave your package without you being there then that will count as a legal signature for them to leave the package without you there and they will then leave the package.