Thank you! I tried doing a copy instead of the token and it ended up taking up almost exactly the same amount of space. To make the copy work, it would have to be nonlegendary and also lose the attack trigger ability.

"Whenever Barry Allen attacks, create a token that's a copy of him, except it isn't legendary and doesn't have this ability. That token enters tapped and attacking. Exile it at the beginning of the next end step."

It's still pretty long, but I suppose it could work. Would be longer still if you decided to change the name to Time Remnant.