A report from the end of 2013 by the WSJ which indicates the ATP approach is working:
At the start of this season, the ATP pushed its chair umpires to crack down on servers’ slow play, by calling more time violations. To make this more palatable to players, and easier to call, the tour tweaked its rulebook. Now servers are docked just a first serve, not a point, for their second and subsequent violation of the rule allowing only 25 seconds between points.
The first violation is essentially just a warning — no penalty. “It doesn’t mean anything,”Carlos Ramos, a veteran chair umpire, told students at an officiating school in Paris last month. And yet, before this season, the rule was rarely enforced, even when most players were flouting it. “Our top chair umpires, they were hesitating” to call time violations, Ramos said. “Even our top chair umpires, we had to coach them a lot. We had to talk to them a lot.”
At the start of the year, officials called time violations with unprecedented regularity. Some players complained, but others didn’t, and nearly all sped up their pace of play, according to the ATP’s own measurements and stats such as average time per point, including time playing the point, this year compared to last year.
This year through the Shanghai tournament last month, umpires had called 659 time violations against servers, 49 of them costing the server a first serve; and 47 violations against returners, costing three points, according to the ATP. For all of last year, umpires called just 59 time violations, and assessed zero point penalties.