You've put your finger on it, Phobos, but you've got it backwards.

It is not the case that as he jumps in time at 88 mph he will cause a large explosion.

The mechanism is set up (and tested with smaller test masses) so that it is "synchronized" with the Earth's surface in spacetime. It could make the jump at any speed--but because of the very effects that you are worried about, it has to be going 88 mph or it will cause an explosion. Actually more of a "blast" in spacetime, but it could still be ugly.

Happened to me once. I experienced puberty for five minutes when I was 43. Whoa.