The runesphere will slowly lose layers regardless of whether or not anyone has siphoned it. Assuming the runesphere starts on the soul layer, it will last for approximately 38 minutes and 37 seconds (2317 seconds) before reverting to its core. It will disappear after 1 hour and 20 seconds (3620 seconds) have passed after it spawns. After it disappears, a new one will spawn in 2 hours 30 minutes and 50 seconds (9050 seconds). They spawn and disappear on each world at the same time, but not necessarily the same location. The spawn phase is depending on the floor number. If it spawns on the top floor, it will usually spawn at Soul phase, middle floor at Chaos phase and bottom floor Body phase.