What Aircraft are you referring to?
On some aircraft the Reverser unlocked warning is triggered by as little as one of four reverser locks not indicating locked.
This means that the reverser doesn't have to move at all to trigger the failure.
A take off would be rejected from low speed when the engine failed to accelerate. Most engines have an interlock that will force idle thrust with a TR failure so when the crew try to set TO thrust the engine would fail to accelerate and the take off would be rejected. The flying pilot would notice the asymmetry immediately so you wouldn't get close to V1.
If a Reverser unlocked during the take off roll the thrust reduction would trigger the rejected take off below V1.