TSandM:I suppose in the worst circumstances, that half second or so might make a difference, but that would mean the person donating had failed to recognize the need for it for quite a long time.
And that is one of the points here isn't it? Watching each other and being comfortable/capable of handling situations. Nothing to do with GUE/DIR. If one diver can not indicate quickly enough that he/she needs gas donated, they have an issue. If they can not handle waiting for a donation more than a few seconds..... they have an issue. If the buddy is not paying attention, they have an issue.....
That half second is not going to make any difference....... both divers have an obligation: one is to notify, the other is to notice.