(a) Beginning on October 1, 1982, child welfare services for children placed voluntarily after January 1, 1982, shall be limited to a period not to exceed 180 days. Subject to the availability of federal funding, voluntary placement services for federally eligible children may be extended for an additional six months, for a total period not to exceed 12 months for either of the following:

1. (1) Families who have a custodial parent or guardian in residential substance abuse treatment who is demonstrating progress that indicates the problems warranting the initial placement are likely to be resolved within the extended time period.
2. (2) Families whose minor child is seriously emotionally disturbed, who requires placement in a residential treatment facility, who otherwise would be likely to be found to fit the description in subdivision (c) of Section 300, and who reasonably may be expected to be returned home within the extended time period.