I may be in the minority, but I think that ball kids should not have to deal with towels. Leave one at the back of the court or on their chair and let the player be in charge of it. If they want to walk back and use it as part of their 25-sec. that is fine. This way there is no complaining about the ball kids taking too long.
Not to mention that it's not the most pleasant thing for a ball kid to have to handle a sweat soaked towel.