In general yes (not so much in my particular case though), but even then entering a new research project, even if it is close to the one you were working on bef

In general yes (not so much in my particular case though), but even then entering a new research project, even if it is close to the one you were working on before still take some non negligible time. But you are right, the time to complete step 1 from my comment may vary a lot and might be short in some cases I guess. In my particular case, I did my PhD on "cryptographic implementation security against physical (side-channel and fault injection) attacks", and my post-doc is on "privacy as control". I chose to apply for this post-doc rather than take one of the few that were offered to me on my PhD topic, because it also interests me scientifically a lot, plus it interests me politically. On the one hand it may have been a bold (or stupid? we'll see that later :)) move career-wise, but on the other hand it was a good time to change topic, as it may be harder to do later when you are even more specialized. And that is not specific to me.