A question for the drivers

So I've been relief driving for a few months now and every time I go out I end up coming back about half an hour to 45 minutes after I'm supposed to... I always leave the yard on time or early if I can get away with it but it's usually traffic or people unpacking slowly that put me behind. Has anyone got any tips as to how I can stop being so late back because it puts the driver who needs the van next behind and means my pay gets messed up. TIA :))