The standby works like this.
if you ask to get on the earlier flight, and there is a seat, you will be moved, if it is full, you can go to the gate that it is boarded from, ask the agent if there is a no show, can I get on.
as soon as the plane is boarded and they are ready to close the doors and all the anoucements have been made trying to find the missing passengers, then, if there are seats they will put you on, you need to be ready to move fast, so stay right around the gate,and it helps if you have no checked luggage.
hope this helps.