Thank you Rory. So that implies that casting spells won't disrupt the seal timer when sitting at 0 seals, and that you will be able to gain seals when repeatedly casting rather than get no benefit from the jewel? If I'm continuously casting, I'll still gain seals if there is less than a 0.71 second time between each cast? Then it will just unleash on the next cast after each .71 second interval?
Yeah, if you had a very slow cast time of 0.72 seconds, you'd get an unleash every cast, effectively a 74% more damage multiplier. If your cast time was 0.5 seconds, it's ~51% more damage per second. The timer starts when you leave maximum seals or when you first equip the support.