The first thing to figure out when determining what time you need to arrive at your hunting spot is shooting time. Shooting time is ½ hour before sunrise and ½ hour after sunset unless stated otherwise by your state.
Since you’ll want to be set up by shooting light, you must figure out the time it takes to get there and how long it will take to put out decoys. It will be up to you to determine travel time and how long the walk is to your spot. If hunting a swamp, typically you will only need 15-30 minutes to put out decoys. If hunting a field, you may need to allow more time depending on the species you’re hunting. Larger goose decoy spreads can take upwards of an hour depending on the size of the spread.
A good rule of thumb is that it’s always best to be earlier than late.