OK, now my 5 cents worth on this one...
Per se, this is an excellent thing. Heavy clan ads spam really is annoying whenever you try to use the wc for either chatting (it happens) or for placing your own ad. I guess that we all may agree on this point, don't we?
However, I do have a few doubts that this will work out the way you intend to...
My reluctance is based on the following points:
1) Looking at the wc on my iDevice, I can't scroll back 5 minutes. So I am virtually blind and have to hope that noone (friend or fiend...) has posted a similar ad into that grey zone. I do compare it to having to drive without a speedometer and risking a speed fine as soon as I am behind the steering wheel.
If you create a rule, give us the tools to observe that rule!
2) While playing, my chats seem to have a certain lag...
I am pretty sure that my game isn't polling the wc every tenth of a second and getting it back instantaneously, I certainly wouldn't call it real-time. So do I really have to say a prayer that noone else will get the brilliant idea to post the same ad as myself whenever I want to advertise? C'mon...
You are in fact going to punish someone not based on his action, but on actions done by his peers, not necessarily under his control.
3) I don't like the punishment people are in for such a petty offence. I predict that at the end of June, you'll have quite a bunch of newbies being perm silenced... and not necessarily out of their own fault. Not sure you'll grow the player base by this.
If you had a mechanism to have a "mild silence" for such offences, you would address this concern. (12/24h wc silence, not counting towards the perm silence counter for example)
4) I have seen a few mods beginning to inform the community via wc and world announcement. Well done!
However, I am not sure that this will be enough to avoid total havoc on June the 7th... Use your system info popup at the app startup to spread the info into the last dark corners of kaw (why not have a clickable link to this announcement thread on it?).
A lot of the success of the introduction of this new rule will depend on the mods. How prepared are mods to deal with this rule? Meisha funnily replied that mods are used to deal with spam every day. Well, well...this might get fun if some mods don't use their brains and just get trigger-happy by pedantically following the new rule. If you ever go down that road, the wc will be unusable the first week of this rule.
I wouldn't mind seeing a grace period of a week, where people would get a warning (a paste on someone's wall or into the wc won't honestly take more time than handling a silence...). In the past, I have seen a few mods (Wabbsy, babycakes, Meisha, to name a few) warning people instead of just pushing the button. Use common sense while applying the TOU, otherwise we might as well implement bots...
Such a grace period would permit both the community as well as the mods to get used to this new rule and accept it.
I have seen a few very interesting ideas for improvement in this thread, especially based around the clan event screen. I hope that those will make it one day.
As for my duty as a clan admin/owner, I will probably deal the following way with ads. If ads are necessary at one moment, designate two advertisers for placing their 2 ads per 5 minutes onto a fixed wc. No other ads permitted (at the risk of getting silenced...).