I know procedures for some companies are to don the life jacket after the aircraft has come to a complete stop.
I have never heard of anything so ridiculous.
You put a life jacket on during the preparation for ditching but do not inflate it.
Looking/feeling around for a life jacket would be the last thing I would want to be doing after ditching. You would need both hands free to go hand over hand to the nearest exit, not one hand holding on the a life jacket and trying to find the exit with the other free hand - especially at night.