The article does, in fact, point that out even though it is written to make the gullible think that all three will be on station all the time. They aren't nuclear-powered, folks, so they can not remain on station for extended periods. One on station, one preparing to replace it, and one back home.
Two mortar shells explode in Golan Heights, no casualties or damage reported (Haaretz)
from the article: Report: Israel to deploy nuclear-armed submarines off Iran coast