Well didn't this thread light up like a christmas tree since last night.
Anyways, How about the common rule everybody has...You PM someone for a challenge, they must ANSWER your PM with the times they are most commonly on-line within 7 days, if they do not, you get an automatic by on their gym. If they do respond to the PM, regaurdless of whether they battle you, or not, then it has been answered. Then you will know when they are on-line. After that, if you are on-line at that gym leaders time that they posted, and they are not, then you win. It is your responsability to PM and challenge a gym leader, but it is their responsability to answer you challenge...they have one week to tell you when the battle can take place, if the gym leader doesn't show up...the challenger wins. (This rule will go into effect in one week, bings it is new, so that everyone can have a chance to read it.)