scala 2 implicit cats type class precendence

precedence.scala

object Precendence {
  import cats.Monoid
  import cats.kernel.Semigroup
  import cats.instances.duration._ // <==== comment this out to see the difference
  implicit val maxDurationSemigroup: Semigroup[Duration] = Semigroup((a, b) => if (a > b) a else b)
  implicit def optionMonoid[A](implicit ev: Semigroup[A]): Monoid[Option[A]] =
    new Monoid[Option[A]] {
      def empty: Option[A] = None
      def combine(x: Option[A], y: Option[A]): Option[A] =
        x match {
          case None => y
          case Some(xx) => y match {
            case None => x
            case Some(yy) => Some(ev.combine(xx,yy))
          }
        }
    }

  def combine(rp1: Option[Duration], rp2: Option[Duration])(implicit mo: Monoid[Option[Duration]]): Option[Duration] = {
    mo.combine(rp1, rp2)
  }

  def main(args: Array[String]): Unit = {

    val rp1 = Some(2.minute)
    val rp2 = Some(90.seconds)

    println(combine(rp1, rp2))
    println(combine(rp1, rp2)(optionMonoid[Duration](maxDurationSemigroup)))
  }
}