When are they out?

[DaveASA/FED]

Ok lets say we have a timing play, BR being tagged at 2nd while R1 is attempting to score with 2 outs. As BR is sliding into 2nd R1 is a step from home, hard slide BU is waiting to see the ball is still controlled....R1 touches home then BU sees control of the ball and comes up with a sell out.

So I ask when is the out an out for the timing of the run scoring? When the tag is first made....or when the BU verifies control was maintained? In this case that difference would mean a run scored or it didn't.