When did the Great Apostacy start according to The Church of Jesus Christ of Latter-day Saints?

Within the theology of the The Church of Jesus Christ of Latter-day Saints, a Great Apostacy is held to. The Great Apostacy is primarily identified by the loss, or removal, of priesthood keys and authority from the earth. I can't find any specifics from a church source on when this occurred. Does anyone know of any detailed explanation on when the apostacy occurred? I'd like to give an idea as to why that is the case, and encourage members to poke holes in it if possible. In our theology, the Apostles hold all the keys of the priesthood, which constitute the right to preside over and direct the Church within a jurisdiction. Sometimes the Apostles delegate those keys. For example, "Bishops hold the priesthood keys to lead the work of the Church in the ward" (local congregation) (source ). "A bishop is called by inspiration of the Lord and ordained by a stake president under the direction of the First Presidency of the Church and the Quorum of the Twelve."(source ) *In the absence of keys held by apostles, there can be no ordination of bishops. A bishop does not hold the keys to authorize the ordination of successor bishop (**this seems to be the key claim**).* As it relates to the Great Apostacy, once the Apostles are all gone, the keys to direct bishop ordination are gone. A bishop could be ordained and alive at the time the last Apostle is taken, and he could ordain others to offices in the Aaronic priesthood, but once he dies the keys he was delegated are gone. So it may be true that holders of the priesthood are alive at the time the last apostle was taken, but within the next 100 years or so, no living key holder will be left and soon following no authoritative ordination will be possible. This seems to be the reason we can't pin a date down, we don't know when the last priesthood holder died. Thoughts?