Ordering direct from GW has never been a guarantee of getting it on release day. Sometimes before but often after. Probably depends on the size of the release as they have the same number of mail order trolls packing so they have to start earlier with bigger releases but still might run late. Do not want a whole bunch of employees sitting around doing nothing all week so that they can push out the door everything on one day.
I've found getting it delivered to my local Games Workshop gets it delivered on time. Because orders I've had delivered to my home have NEVER arrived on time.Not sure if a local GW is an option for you, but if you can you don't pay postage and packaging to have it delivered there.