code: func GetIPAddressLeaseTime(o dhcp4.Options) (time.Duration, error) {
  	v := o.Get(dhcp4.OptionIPAddressLeaseTime)
  	if v == nil {
  		return 0, dhcp4.ErrOptionNotPresent
  	}
  	var u Uint32
  	return time.Duration(u) * time.Second, (&u).UnmarshalBinary(v)
  }
docs: // GetIPAddressLeaseTime returns the proposed lease time.
  //
  // The IP address lease time message is defined by RFC 2132, Section 9.2.