Since human behavior isn’t something that can be predicted in any precise manner, I don’t think there’s any one particular answer for this question.
There are multiple reasons for the length of time it takes a narcissist to hoover after the initial devaluation and discard. There’s also no absolute guarantee that the narc will hoover a particular victim.
Contrary to popular belief, narcissists don’t hoover every single one of their victims. It all depends on the individual narc, whether or not they think a victim is worth hoovering.
I have personally been hoovered by a covert narc ex-boyfriend several years after the discard. I’ve also been hoovered multiple times by my Malignant Narcissist ex-husband relatively quickly , as well as after lengthy periods of time.
Hoovering had been a pattern for him throughout the years. After extensively educating myself about Narcissism, and particularly Malignant Narcissists, I knew when I made my final escape that he would eventually attempt to hoover me again.
Which he did.
But I didn’t know when it was going to happen.
The behavior patterns of an individual narcissist, with a particular victim, can predict somewhat accurately if the narc will hoover.
But not when they will hoover.