A person at risk, or a parent or legal guardian of a minor who is a person at risk, may accept or reject a qualified offer made under this part as provided in this section. Subject to the provisions of § 6-833 of this subtitle, a person at risk, or a parent or legal guardian of a minor who is a person at risk, may accept a qualified offer within 30 days after receipt of the qualified offer unless the parties agree otherwise. Subject to the provisions of § 6-833 of this subtitle and unless the parties agree otherwise, an offer which is not accepted within 30 days following receipt shall be deemed to have been rejected.