I don't know where you got the idea it's 3CP. The only errata for Tide of Traitors (for the first printing of the codex, the second printing has the errata'd version) is
Page 159 – Tide of Traitors
Add the following sentence:
‘You can only use this Stratagem once per battle.’
Nothing prevents you using it turn 1. Not sure where that idea comes from either.
If I may ask, why would you think it's 3CP and can't be used turn 1?