X seconds between repetitions of suutra-s. Why? As to the YF suutra, almost all of us know by now, that YF (aakaasha-gamanam) is based on the Meissner effect, like a magnet levitating above a superconductor (but Earth is the magnet and an yffer is the superconducting lump of meat and stuff).
Now, that X seconds allows the suutra transcend "down" to the QM-level of electromagnetism and activate(?) the photons?? A photon, of course, is the force carrier for the EMF! That's why the suutra following YFS mentions "prakaashaavaraNakSayaH", (prakaasha-aavaraNa-kSayaH,"light-covering-destruction", destruction of the covering of light)?? RO-FFL-OL!