User blog comment:Pawn of Atlas/Important Discussion for Rapture Storyline page/@comment-75.36.142.227-20140329223049/@comment-75.36.140.200-20140403005417

'Knowing Fontaine, it's likely he began planning his role as Atlas very quickly after his "death" '

More likely he planned alot BEFORE  (he was cosmetically changed to look the part) including pulling assets out of his smuggling operation and certainly supplies/weapons/personnel  (we see alot of those in Fontaine's in the DLC)

'would take some time to plan'

Yet the DLC shows some flunky assigned to pick targets and locked up in the department store makes it a bit hard to carry through any specific plans made alot earlier.