The Bad Day
The concept of "leap year" does odd things to the Symphony. It all apparently stems back to a particularly acrimonious debate - at least, by the standards of the time - where certain Archangels had arguments with certain other Archangels over the need to completely synchronize the various likely methods of keeping time. One set argued that making everything align was aesthetically pleasing, and was thus obviously the superior solution; the other made the counterpoint that it was going to be hard enough to encourage belief in the illusion that the universe was unplanned. Giving supporters of the teleological argument more justification for their stance was eventually decided to be ultimately counterproductive, which is why humanity has a circadian rhythm that is somewhat "off" from Earth's 24 hour cycle... and why the full year is just a little bit over 365 days.
While this is no doubt good for the development of secular thinking, it's a metaphysical pain in the nether regions for celestials. The periodic need to reconcile the calendar creates odd eddies in the Symphony on the days that said reconciliation takes place - eddies that hamper. In game terms, all invocations on leap year days are at -3, and Essence use generates one extra note of disturbance. Those with Celestial Discord get a -1 to their CD to determine Essence generation. Finally, celestials simply feel rotten on days like this. This can have more significant effects on the War than all of the above put together. Oddly enough, Symphonically Aware human beings get an extra note of Essence on leap year days, and are often infuriatingly chipper. If injured, they also get one extra hit healed at noon.
The contrast is notable, but not often noted. By either side.