145,
Yes, the calculations of V1 include this buffer, but that does not mean it should be used. We always have buffers built into the performance figures, but we then try and not eat into them.
You do not have one or two seconds after V1 to initiate an RTO. If it has not been initiated by V1, the takeoff should be continued unless the aircraft is unflyable.
MGC is correct in saying that a failure close to V1, with insufficient time to react and initiate an RTO before V1, should be taken into the air.