I bought a 40" w4500, the info referring to the w4000 comes from searching online, my guess is the standby time is similar if not the same on the w4500. If yours seems random I'm not sure why that may be but play it by ear.
My sets fault was a loud intermittent buzz coming from the top of the TV. Possibly a loose transformer but I'm not taking any chances, I've heard nothing but bad about the company I bought it from since.
The set was my treat as I'm not active through disability and constant severe pain, typical of my luck to get a faulty TV lol