So, I'm watching Safin vs Clement. Clement hits a serve; it's called out. He walks up to the net, looks at the place it landed (looking for a mark), stared at it for 5 seconds or so, then challenges. Later, Safin thinks about whether to challenge or not, and the umpire tells him it's too late to challenge, he took too long to decide, or something like that; either way, there was a conversation with the umpire about the challenges. He got the information that the challenge needs to be done "relatively quickly" (umpire's words). Commentators immediately want to know what's the definition of "relatively quickly", and it seemed like Safin did as well; commentators got one of their guys down on court to talk to the Tournament Supervisor, Safin stopped by to have a chat as well. His response - "well, the decision to challenge or not needs to be made immediately." When it was pointed out ot him that Clement clearly took some time to decide, he responded with something along the lines of "Well, they have a bit of time," leaving both me, the commentators, and Safin completely hanging as to what "immediately" means and HOW LONG DO THEY ACTUALLY GET to decide whether to challenge or not. Ugh, no wonder some players are against the challenge system.