V1 is scheduled after Vef. The time gap depends on the certification standard. The gap is already in the calculation so you need to make the first action to stop at or before V1.
If you make the decision to go before V1 you will compromise your screen height.
If you make the first action to stop after V1 you will compromise your stopping distance.
This is for the engine failure case only, and when at your max take off weight balanced field length limited.
Other cases will be different.
It is possible to include stopping distance allowance to hedge the stopping case and of course line up allowance must be used where necessary.
It's just not black and white.