It needs to be something short of V1 where you have time to react. At V1, you're committed.
If you reach "time to V1" before V1, you are not at V1 by definition.
The only way it can work is if you abort once the time is reached, before V1 - if you wait until V1 and say "that took too long" you don't have the stopping distance that was used for the V1 calculation. If you reach "time to V1" before V1 and continue, you can be sure that at some point you will be below V1 without distance to stop - because the calculated stopping distance is used up by slower acceleration.
And it can't be a rule of thumb - it has to be a hard go/nogo number like V1, output from the V1 calculation.