In general, We can consider that at worst 1ms is added to
  ipv4 response, due the usage of openvpn.

  We can also consider that we accept a certain increase
  on latency for various reasons, if we are on a
  congested link. So we can consider that 10% is
  reseonable enough.

  The goal of this promise it to detect the real slowliness, rather
  them minor temporary failures, due internet oscilation.