The triggerable has a cooldown of 950ms on Fire Brand. I believe what this means is that the triggerable is only going to attempt to cast the skill every 950ms, whether or not the target is burning. If the target isn't burning, the proc won't cast, but you'll still have to wait the 950ms for another chance for the triggerable to activate. It's not a huge issue, but certainly bears consideration for your own skills.
I did not fully understood the problem... can't you set the triggerable to trigger as often as possible but the proc skill's cooldown as high as you want it to be?Oh yea, that might work too. I forgot that proc can have a cooldown, silly me. Thanks for the SUBTYPE list.
What conditions you want for that skill
here's the dropdown list from inside GUTS: