There is no way, no how any umpire would have the guts to call a time violation and take a point in a match of this significance. I mean, a lot of time is spent waiting for the crowd to shut up. If the umpire cannot control the crowd (and he can't), then you can't hold the players to 20 seconds.
It would have been interesting had Fed started complaining about it to the umpire. But he didn't. You have to let the players play.
Were there times when Nadal wasn't ready when Fed wanted to serve? Fed was moving awfully fast toward the end. Too fast for his own good, maybe . . .