Except where a minor is in custody, any hearing on a petition filed pursuant to Article 8 (commencing with Section 325) of this chapter may be continued by the court for not more than 10 days in addition to any other continuance authorized in this chapter whenever the court is satisfied that an unavailable and necessary witness will be available within such time. If the court knows or has reason to know that the child is an Indian child, the failure to retain in a timely manner the services of a qualified expert witness shall not, in and of itself, demonstrate that a necessary witness is unavailable.