I’m sure it took you more than a week to become the supreme leader’s right hand man.
Not really. Snoke just assumed he would be the next Vader. He encouraged Kylo’s turn so I imagine his rise to power was a walk in the park. Snoke never thought anyone would even think to betray him.
So while he did bid his time, I do think he could of done this whole change within a month if he had wanted.