When did Nathaniel Essex clone himself?

[Midnighter]

When were Mister Sinister, Doctor Stasis, Orbis Stellaris, and Mother Righteous cloned?
Nathaniel Essex is transformed by Apolypse in FACY&PHX in 1859, and his next appearance would be in New York City in 1891 (Gam3 13-14) as Nathan Milbury, where he meets time travelers Gambit and Courier, assimilating the latter's powers.

Immortal X-Men 8 takes place in 1895 London and features the death of the original Nathaniel Essex and Destiny's discovery of cloning tanks. But we do not know how long ago the clones were created.

My impression is that the Nathan Milbury who is active in New York in 1891 and gains shape-shifting powers (which the other clones do not possess) is already the cloned Mr. Sinister and not the original Nathaniel Essex. In my opinion, Essex's plan to clone himself into four separate beings to obtain the knowledge needed to become a Dominion should predate 1891. It probably must have originated around Darwin's death in 1882.

By 1899, however, Mr. Sinister would return to London to attend the Enigma Variations at St. James Hall, on the same occasion that Destiny has visions of the future.