said by txdust :

I use to be a tech support for Uverse and would get called on this daily. The issue is you have a number of streams all independent from each other. When you turn on a receiver box that box in essence raises its hand to grab a stream. When a second box is turned on even on the same channel that box takes claim to a different stream. If your watching the game in the living room, and your son is watching the game in his room, think of the 2 TV's to be working on separate service. Which mean they travel from the AT&T center all the way to your V-rad box, than to your house. The greater the distance between you and the AT&t service center the great chance for these signals to unsync and be on an independent time line signal wise. This is not like your co-ax cable which is split at your house to separate rooms, where the unsync is too small to notice. This is caused by miles of traffic and unseen interference.

said by ILpt4U :

The scenario as it is described here is just not true. If 2 TVs in one house are watching the same channel, it is one stream being MultiCast to multiple boxes.

The reason the first TV is slower, is because it began the stream as UniCast -- It takes some measure of time (though pretty quick) for the STB to request to join the Multicast, be it at the VRAD, CO, or higher level, so to achieve instant channel changes, the streams always start Unicast, and is handed off to Multicast

The Second TV doesn't have to ask for the Multicast, because it is already present on the LAN, and it is able to join an in-progress Multicast stream that is already there. Same with a 3rd, 4th, 5th, etc. So those additional TVs don't have that slight delay where the buffer is on the 1st TV from the Unicast-to-Multicast handoff.