Generally physical echoes have to start setting in immediately. It is however up to the player how fast the effect comes to completion. Walter may feel the world slow down around him from one second to the next, or it might gradually slow down around him over a couple of hours, days, weeks or even months.

So no to a delayed trigger for physical regains, but that doesn't mean that it has to be immediate in its entirety and thus might not feel immediate to the person experiencing it.