there was an interesting point during Chakvetadze-Radwanska match when Aga, after let's say 4 or 5 seconds, decided to use challenge but was not allowed to as if it was too late
as the Polish commentator said, you could think of Henin or Sharapova taking much more time to think about the challenge and 'cosult' their coaches before making the decision
do you think it was just accidental or there is simply no equal treatment of the biggest stars and the rest?
Urszula Radwańska Kasia Piter Magda Linette Paula Kania
also it depends on when the challenge happens. if its say on an ace then more time will be allowed than middle of a rally. i think the reason aga was denied the challenge was that she hit her shot then (because it had loop on it) recovered her position middle of the court to carry on the rally but her shot drifted wide. h ad she have held her hand up and said challenge straight after hitting the shot and not recovering position and see where her ball bounces, then she would have been able to challenge. like others have said its down to the umpire some are more forgiving than others.
i personaly think challenges should be instant, no looking at the mark or checking with their box. you either challenge straight away of lose the right to.