Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Type
CHR_TYPEParameter: Time Factor
CHR_TFACParameter: Variation
CHR_TVARParameter: On
IN_CHR_ONParameter: Animation Time
IN_CHR_ATIMEParameter: Time
OUT_CHR_TIME