The title says it all.
First post on exploit section (please be nice ).
1) Summon the Guild Herald
2) Relog if you want it
To be honest i don't really know how it works.. Porting out makes him go away but relogging makes him reappear. You must not summon any other pet or he'll go and the cooldown will apply.
Clicking on another pet in the pet window will summon the other pet, even if you don't click summon, so don't click
If you don't summon another pet the cooldown will not decrease and you can see the Guild Herald and Guild Page on cooldown even 4 hours after summoning it, but at any time, relog and you'll see him again.
(i can't make screenshot atm, i had it summoned yesterday and he was still there this morning but i clicked Miniwing so i have to wait 4hours to post screenshots.. I did it twice so i'm pretty sure it's a bug and not something that happens only one time)
It seems to be working on any pet but the guild herald is definitely the only pet that has an use for it.