I guess arguments can be made on both sides.
If you announce a release time (or hour range) then you almost guarantee those first hours possibly overloading your servers. However, at least they can prepare for that, right?
On the other hand, if you don't announce a release time, you risk infuriating (but most likely not alienating) your customer base, right? Also, by announcing it in advance (at 4:00 AM EDT, for example) you might have a huge hit right away, but that would almost guarantee that the normal "peak" hour traffic would be mitigated, right?
I dunno. I'm an impatient child. I've a busy day tomorrow, won't be near a computer and I just *want it now*!