The timer on the Chronivac was set to one million. But it wasn't years, it was seconds.
So that means Jeff would turn back in about 11 and a half days. Provided nothing happened to his current status
as a grain of sand and he was in a safe place to turn back. The Chronivac had a nice in built safety that
wouldn't turn inanimates back to flesh and blood if they were somewhere that would be fatal.
Oh, but 11 and a half days is plenty of time for something to happen to a grain of sand. Be pulled into the sea,
ingested by something, melted with countless other grains of sand into glass. And many other possibilities.