10 seconds is a guess but you would absolutely add on time.
As soon as a point ends, a ballchild instantly hands a new ball/towel to the player while another runs on and collects the ball, it all happens while the player is readying the next shot.
If the player had to jog and collect the ball, then jog and get a towel, then towel himself off, then get ready for the next shot, it definitely adds time.