Ceph do you realise that a slow pokémon with this ability and access to at least one of the dig-like moves would be literally untouchable right? I know you intended the ability for mega espeon primarily, but the implications of it in the case of, say, a skill swap, are scary as fuck.
Say for example that I skill swap it into a marowak holding a lagging tail: marowak is already slow on its own, but the lagging tail makes it always move last when it uses a move of the same priority as the opponent. Now, it gains the ability to select dig and becomes invulnerable to literally any form of attack or direct damage except earthquake, with a +7 priority charge that prevents even moves like extreme speed from hitting and shuts the lagging tail down as no other move has the same priority bracket. However, when the time to attack comes, marowak's dig will still and always come in last place, as the lagging tail makes everything else on the field move before marowak's dig hits, at the end of the turn. Basically if it wasn't because dig can't hit flying types, EQ will hit underground marowak for double the damage, dig itself has only 10 PP and rare no guard foes can still hit.... this would be literally broken. I still think it is, kinda. When you have to resort to obscure negative priority attacks (vital throw, avalanche, revenge) to hit, then there's a problem.
A mon with access to fly in the same circumstances as the marowak above is literally a god, as it cannot be touched by any attack unless it runs out of fly PP (which could always be helped by a teammate with lunar dance), and nothing is immune to the flying type. The opponent has to resort to either toxic stall before the mon acquires the ability (assuming this is a double battle and you skill swapped time paradox into it), or rely on damaging weather, ghost curse, having an excellent wall that can PP stall, or just forfeit.
In doubles particularly this would be a nightmare of an ability that would probably get banned depending on what mons get it, as I'm pretty sure some specific partner combinations can win the game by simply leading with them.